| Message ID | 20210621165230.4.Id84a954e705fcad3fdb35beb2bc372e4bf2108c7@changeid |
|---|---|
| State | New |
| Headers | show |
| Series | iommu: Enable devices to request non-strict DMA, starting with QCom SD/MMC | expand |
On 6/22/21 7:52 AM, Douglas Anderson wrote: > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) > > static int iommu_group_alloc_default_domain(struct bus_type *bus, > struct iommu_group *group, > - unsigned int type) > + unsigned int type, > + struct device *dev) > { > struct iommu_domain *dom; > > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, > if (!dom) > return -ENOMEM; > > + /* Save the strictness requests from the device */ > + if (dev && type == IOMMU_DOMAIN_DMA) { > + dom->request_non_strict = dev->request_non_strict_iommu; > + dom->force_strict = dev->force_strict_iommu; > + } > + An iommu default domain might be used by multiple devices which might have different "strict" attributions. Then who could override who? Best regards, baolu
On Mon, Jun 21, 2021 at 4:53 PM Douglas Anderson <dianders@chromium.org> wrote: > > In the patch ("drivers: base: Add bits to struct device to control > iommu strictness") we add the ability for devices to tell us about > their IOMMU strictness requirements. Let's now take that into account > in the IOMMU layer. > > A few notes here: > * Presumably this is always how iommu_get_dma_strict() was intended to > behave. Had this not been the intention then it never would have > taken a domain as a parameter. > * The iommu_set_dma_strict() feels awfully non-symmetric now. That > function sets the _default_ strictness globally in the system > whereas iommu_get_dma_strict() returns the value for a given domain > (falling back to the default). Presumably, at least, the fact that > iommu_set_dma_strict() doesn't take a domain makes this obvious. > > The function iommu_get_dma_strict() should now make it super obvious > where strictness comes from and who overides who. Though the function > changed a bunch to make the logic clearer, the only two new rules > should be: > * Devices can force strictness for themselves, overriding the cmdline > "iommu.strict=0" or a call to iommu_set_dma_strict(false)). > * Devices can request non-strictness for themselves, assuming there > was no cmdline "iommu.strict=1" or a call to > iommu_set_dma_strict(true). > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > drivers/iommu/iommu.c | 56 +++++++++++++++++++++++++++++++++---------- > include/linux/iommu.h | 2 ++ > 2 files changed, 45 insertions(+), 13 deletions(-) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 808ab70d5df5..0c84a4c06110 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -28,8 +28,19 @@ > static struct kset *iommu_group_kset; > static DEFINE_IDA(iommu_group_ida); > > +enum iommu_strictness { > + IOMMU_DEFAULT_STRICTNESS = -1, > + IOMMU_NOT_STRICT = 0, > + IOMMU_STRICT = 1, > +}; > +static inline enum iommu_strictness bool_to_strictness(bool strictness) > +{ > + return (enum iommu_strictness)strictness; > +} > + > static unsigned int iommu_def_domain_type __read_mostly; > -static bool iommu_dma_strict __read_mostly = true; > +static enum iommu_strictness cmdline_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > +static enum iommu_strictness driver_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > static u32 iommu_cmd_line __read_mostly; > > struct iommu_group { > @@ -69,7 +80,6 @@ static const char * const iommu_group_resv_type_string[] = { > }; > > #define IOMMU_CMD_LINE_DMA_API BIT(0) > -#define IOMMU_CMD_LINE_STRICT BIT(1) > > static int iommu_alloc_default_domain(struct iommu_group *group, > struct device *dev); > @@ -336,25 +346,38 @@ early_param("iommu.passthrough", iommu_set_def_domain_type); > > static int __init iommu_dma_setup(char *str) > { > - int ret = kstrtobool(str, &iommu_dma_strict); > + bool strict; > + int ret = kstrtobool(str, &strict); > > if (!ret) > - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; > + cmdline_dma_strict = bool_to_strictness(strict); > return ret; > } > early_param("iommu.strict", iommu_dma_setup); > > void iommu_set_dma_strict(bool strict) > { > - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) > - iommu_dma_strict = strict; > + /* A driver can request strictness but not the other way around */ > + if (driver_dma_strict != IOMMU_STRICT) > + driver_dma_strict = bool_to_strictness(strict); > } > > bool iommu_get_dma_strict(struct iommu_domain *domain) > { > - /* only allow lazy flushing for DMA domains */ > - if (domain->type == IOMMU_DOMAIN_DMA) > - return iommu_dma_strict; > + /* Non-DMA domains or anyone forcing it to strict makes it strict */ > + if (domain->type != IOMMU_DOMAIN_DMA || > + cmdline_dma_strict == IOMMU_STRICT || > + driver_dma_strict == IOMMU_STRICT || > + domain->force_strict) > + return true; > + > + /* Anyone requesting non-strict (if no forces) makes it non-strict */ > + if (cmdline_dma_strict == IOMMU_NOT_STRICT || > + driver_dma_strict == IOMMU_NOT_STRICT || > + domain->request_non_strict) > + return false; > + > + /* Nobody said anything, so it's strict by default */ If iommu.strict is not set in the command line, upstream treats it as iommu.strict=1. Meaning, no drivers can override it. If I understand it correctly, with your series, if iommu.strict=1 is not set, drivers can override the "default strict mode" and ask for non-strict mode for their domain. So if this series gets in and future driver changes start asking for non-strict mode, systems that are expected to operate in fully strict mode will now have devices operating in non-strict mode. That's breaking backward compatibility for the kernel command line param. It looks like what you really need is to change iommu.strict from 0/1 to lazy (previously 0), strict preferred, strict enforced (previously 1) and you need to default it to "enforced". Alternately (and potentially a better option?), you really should be changing/extending dev_is_untrusted() so that it applies for any struct device (not just PCI device) and then have this overridden in DT (or ACPI or any firmware) to indicate a specific device is safe to use non-strict mode on. What you are trying to capture (if the device safe enough) really isn't a function of the DMA device's driver, but a function of the DMA device. > return true; > } > EXPORT_SYMBOL_GPL(iommu_get_dma_strict); > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) > > static int iommu_group_alloc_default_domain(struct bus_type *bus, > struct iommu_group *group, > - unsigned int type) > + unsigned int type, > + struct device *dev) > { > struct iommu_domain *dom; > > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, > if (!dom) > return -ENOMEM; > > + /* Save the strictness requests from the device */ > + if (dev && type == IOMMU_DOMAIN_DMA) { > + dom->request_non_strict = dev->request_non_strict_iommu; > + dom->force_strict = dev->force_strict_iommu; > + } > + > group->default_domain = dom; > if (!group->domain) > group->domain = dom; > @@ -1550,7 +1580,7 @@ static int iommu_alloc_default_domain(struct iommu_group *group, > > type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type; > > - return iommu_group_alloc_default_domain(dev->bus, group, type); > + return iommu_group_alloc_default_domain(dev->bus, group, type, dev); > } > > /** > @@ -1721,7 +1751,7 @@ static void probe_alloc_default_domain(struct bus_type *bus, > if (!gtype.type) > gtype.type = iommu_def_domain_type; > > - iommu_group_alloc_default_domain(bus, group, gtype.type); > + iommu_group_alloc_default_domain(bus, group, gtype.type, NULL); > > } > > @@ -3130,7 +3160,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group, > } > > /* Sets group->default_domain to the newly allocated domain */ > - ret = iommu_group_alloc_default_domain(dev->bus, group, type); > + ret = iommu_group_alloc_default_domain(dev->bus, group, type, dev); > if (ret) > goto out; > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 32d448050bf7..0bddef77f415 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -81,6 +81,8 @@ struct iommu_domain_geometry { > > struct iommu_domain { > unsigned type; > + bool force_strict:1; > + bool request_non_strict:1; > const struct iommu_ops *ops; > unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */ > iommu_fault_handler_t handler; > -- > 2.32.0.288.g62a8d224e6-goog >
On 2021-06-22 00:52, Douglas Anderson wrote: > In the patch ("drivers: base: Add bits to struct device to control > iommu strictness") we add the ability for devices to tell us about > their IOMMU strictness requirements. Let's now take that into account > in the IOMMU layer. > > A few notes here: > * Presumably this is always how iommu_get_dma_strict() was intended to > behave. Had this not been the intention then it never would have > taken a domain as a parameter. FWIW strictness does have the semantic of being a per-domain property, but mostly in the sense that it's only relevant to IOMMU_DOMAIN_DMA domains, so the main thing was encapsulating that check rather than duplicating it all over callsites. > * The iommu_set_dma_strict() feels awfully non-symmetric now. That > function sets the _default_ strictness globally in the system > whereas iommu_get_dma_strict() returns the value for a given domain > (falling back to the default). Presumably, at least, the fact that > iommu_set_dma_strict() doesn't take a domain makes this obvious. It *is* asymmetric - one is for IOMMU core code and individual driver internals to know whether they need to do whatever bits of setting up a flush queue for a given domain they are responsible for, while the other is specifically for two drivers to force the global default in order to preserve legacy driver-specific behaviour. Maybe that should have been called something like iommu_set_dma_default_strict instead... :/ Robin. > The function iommu_get_dma_strict() should now make it super obvious > where strictness comes from and who overides who. Though the function > changed a bunch to make the logic clearer, the only two new rules > should be: > * Devices can force strictness for themselves, overriding the cmdline > "iommu.strict=0" or a call to iommu_set_dma_strict(false)). > * Devices can request non-strictness for themselves, assuming there > was no cmdline "iommu.strict=1" or a call to > iommu_set_dma_strict(true). > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > drivers/iommu/iommu.c | 56 +++++++++++++++++++++++++++++++++---------- > include/linux/iommu.h | 2 ++ > 2 files changed, 45 insertions(+), 13 deletions(-) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 808ab70d5df5..0c84a4c06110 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -28,8 +28,19 @@ > static struct kset *iommu_group_kset; > static DEFINE_IDA(iommu_group_ida); > > +enum iommu_strictness { > + IOMMU_DEFAULT_STRICTNESS = -1, > + IOMMU_NOT_STRICT = 0, > + IOMMU_STRICT = 1, > +}; > +static inline enum iommu_strictness bool_to_strictness(bool strictness) > +{ > + return (enum iommu_strictness)strictness; > +} > + > static unsigned int iommu_def_domain_type __read_mostly; > -static bool iommu_dma_strict __read_mostly = true; > +static enum iommu_strictness cmdline_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > +static enum iommu_strictness driver_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > static u32 iommu_cmd_line __read_mostly; > > struct iommu_group { > @@ -69,7 +80,6 @@ static const char * const iommu_group_resv_type_string[] = { > }; > > #define IOMMU_CMD_LINE_DMA_API BIT(0) > -#define IOMMU_CMD_LINE_STRICT BIT(1) > > static int iommu_alloc_default_domain(struct iommu_group *group, > struct device *dev); > @@ -336,25 +346,38 @@ early_param("iommu.passthrough", iommu_set_def_domain_type); > > static int __init iommu_dma_setup(char *str) > { > - int ret = kstrtobool(str, &iommu_dma_strict); > + bool strict; > + int ret = kstrtobool(str, &strict); > > if (!ret) > - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; > + cmdline_dma_strict = bool_to_strictness(strict); > return ret; > } > early_param("iommu.strict", iommu_dma_setup); > > void iommu_set_dma_strict(bool strict) > { > - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) > - iommu_dma_strict = strict; > + /* A driver can request strictness but not the other way around */ > + if (driver_dma_strict != IOMMU_STRICT) > + driver_dma_strict = bool_to_strictness(strict); > } > > bool iommu_get_dma_strict(struct iommu_domain *domain) > { > - /* only allow lazy flushing for DMA domains */ > - if (domain->type == IOMMU_DOMAIN_DMA) > - return iommu_dma_strict; > + /* Non-DMA domains or anyone forcing it to strict makes it strict */ > + if (domain->type != IOMMU_DOMAIN_DMA || > + cmdline_dma_strict == IOMMU_STRICT || > + driver_dma_strict == IOMMU_STRICT || > + domain->force_strict) > + return true; > + > + /* Anyone requesting non-strict (if no forces) makes it non-strict */ > + if (cmdline_dma_strict == IOMMU_NOT_STRICT || > + driver_dma_strict == IOMMU_NOT_STRICT || > + domain->request_non_strict) > + return false; > + > + /* Nobody said anything, so it's strict by default */ > return true; > } > EXPORT_SYMBOL_GPL(iommu_get_dma_strict); > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) > > static int iommu_group_alloc_default_domain(struct bus_type *bus, > struct iommu_group *group, > - unsigned int type) > + unsigned int type, > + struct device *dev) > { > struct iommu_domain *dom; > > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, > if (!dom) > return -ENOMEM; > > + /* Save the strictness requests from the device */ > + if (dev && type == IOMMU_DOMAIN_DMA) { > + dom->request_non_strict = dev->request_non_strict_iommu; > + dom->force_strict = dev->force_strict_iommu; > + } > + > group->default_domain = dom; > if (!group->domain) > group->domain = dom; > @@ -1550,7 +1580,7 @@ static int iommu_alloc_default_domain(struct iommu_group *group, > > type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type; > > - return iommu_group_alloc_default_domain(dev->bus, group, type); > + return iommu_group_alloc_default_domain(dev->bus, group, type, dev); > } > > /** > @@ -1721,7 +1751,7 @@ static void probe_alloc_default_domain(struct bus_type *bus, > if (!gtype.type) > gtype.type = iommu_def_domain_type; > > - iommu_group_alloc_default_domain(bus, group, gtype.type); > + iommu_group_alloc_default_domain(bus, group, gtype.type, NULL); > > } > > @@ -3130,7 +3160,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group, > } > > /* Sets group->default_domain to the newly allocated domain */ > - ret = iommu_group_alloc_default_domain(dev->bus, group, type); > + ret = iommu_group_alloc_default_domain(dev->bus, group, type, dev); > if (ret) > goto out; > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 32d448050bf7..0bddef77f415 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -81,6 +81,8 @@ struct iommu_domain_geometry { > > struct iommu_domain { > unsigned type; > + bool force_strict:1; > + bool request_non_strict:1; > const struct iommu_ops *ops; > unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */ > iommu_fault_handler_t handler; >
Hi, On Mon, Jun 21, 2021 at 7:56 PM Saravana Kannan <saravanak@google.com> wrote: > > On Mon, Jun 21, 2021 at 4:53 PM Douglas Anderson <dianders@chromium.org> wrote: > > > > In the patch ("drivers: base: Add bits to struct device to control > > iommu strictness") we add the ability for devices to tell us about > > their IOMMU strictness requirements. Let's now take that into account > > in the IOMMU layer. > > > > A few notes here: > > * Presumably this is always how iommu_get_dma_strict() was intended to > > behave. Had this not been the intention then it never would have > > taken a domain as a parameter. > > * The iommu_set_dma_strict() feels awfully non-symmetric now. That > > function sets the _default_ strictness globally in the system > > whereas iommu_get_dma_strict() returns the value for a given domain > > (falling back to the default). Presumably, at least, the fact that > > iommu_set_dma_strict() doesn't take a domain makes this obvious. > > > > The function iommu_get_dma_strict() should now make it super obvious > > where strictness comes from and who overides who. Though the function > > changed a bunch to make the logic clearer, the only two new rules > > should be: > > * Devices can force strictness for themselves, overriding the cmdline > > "iommu.strict=0" or a call to iommu_set_dma_strict(false)). > > * Devices can request non-strictness for themselves, assuming there > > was no cmdline "iommu.strict=1" or a call to > > iommu_set_dma_strict(true). > > > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > --- > > > > drivers/iommu/iommu.c | 56 +++++++++++++++++++++++++++++++++---------- > > include/linux/iommu.h | 2 ++ > > 2 files changed, 45 insertions(+), 13 deletions(-) > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > > index 808ab70d5df5..0c84a4c06110 100644 > > --- a/drivers/iommu/iommu.c > > +++ b/drivers/iommu/iommu.c > > @@ -28,8 +28,19 @@ > > static struct kset *iommu_group_kset; > > static DEFINE_IDA(iommu_group_ida); > > > > +enum iommu_strictness { > > + IOMMU_DEFAULT_STRICTNESS = -1, > > + IOMMU_NOT_STRICT = 0, > > + IOMMU_STRICT = 1, > > +}; > > +static inline enum iommu_strictness bool_to_strictness(bool strictness) > > +{ > > + return (enum iommu_strictness)strictness; > > +} > > + > > static unsigned int iommu_def_domain_type __read_mostly; > > -static bool iommu_dma_strict __read_mostly = true; > > +static enum iommu_strictness cmdline_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > > +static enum iommu_strictness driver_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > > static u32 iommu_cmd_line __read_mostly; > > > > struct iommu_group { > > @@ -69,7 +80,6 @@ static const char * const iommu_group_resv_type_string[] = { > > }; > > > > #define IOMMU_CMD_LINE_DMA_API BIT(0) > > -#define IOMMU_CMD_LINE_STRICT BIT(1) > > > > static int iommu_alloc_default_domain(struct iommu_group *group, > > struct device *dev); > > @@ -336,25 +346,38 @@ early_param("iommu.passthrough", iommu_set_def_domain_type); > > > > static int __init iommu_dma_setup(char *str) > > { > > - int ret = kstrtobool(str, &iommu_dma_strict); > > + bool strict; > > + int ret = kstrtobool(str, &strict); > > > > if (!ret) > > - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; > > + cmdline_dma_strict = bool_to_strictness(strict); > > return ret; > > } > > early_param("iommu.strict", iommu_dma_setup); > > > > void iommu_set_dma_strict(bool strict) > > { > > - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) > > - iommu_dma_strict = strict; > > + /* A driver can request strictness but not the other way around */ > > + if (driver_dma_strict != IOMMU_STRICT) > > + driver_dma_strict = bool_to_strictness(strict); > > } > > > > bool iommu_get_dma_strict(struct iommu_domain *domain) > > { > > - /* only allow lazy flushing for DMA domains */ > > - if (domain->type == IOMMU_DOMAIN_DMA) > > - return iommu_dma_strict; > > + /* Non-DMA domains or anyone forcing it to strict makes it strict */ > > + if (domain->type != IOMMU_DOMAIN_DMA || > > + cmdline_dma_strict == IOMMU_STRICT || > > + driver_dma_strict == IOMMU_STRICT || > > + domain->force_strict) > > + return true; > > + > > + /* Anyone requesting non-strict (if no forces) makes it non-strict */ > > + if (cmdline_dma_strict == IOMMU_NOT_STRICT || > > + driver_dma_strict == IOMMU_NOT_STRICT || > > + domain->request_non_strict) > > + return false; > > + > > + /* Nobody said anything, so it's strict by default */ > > If iommu.strict is not set in the command line, upstream treats it as > iommu.strict=1. Meaning, no drivers can override it. > > If I understand it correctly, with your series, if iommu.strict=1 is > not set, drivers can override the "default strict mode" and ask for > non-strict mode for their domain. So if this series gets in and future > driver changes start asking for non-strict mode, systems that are > expected to operate in fully strict mode will now have devices > operating in non-strict mode. > > That's breaking backward compatibility for the kernel command line > param. It looks like what you really need is to change iommu.strict > from 0/1 to lazy (previously 0), strict preferred, strict enforced > (previously 1) and you need to default it to "enforced". I'm not quite sure I'd agree, but certainly it could be up for debate. I think I'm keeping full compatibility with the kernel command line parameter, specifically: * iommu.strict=0: default to non-strict mode unless a driver overrides * iommu.strict=1: force everything to strict no matter what ...both of those two things are the same before and after my patchset. You're arguing that I'm changing the behavior of the system when no command line parameter is present. To me this seems a little bit of a stretch. If no command line parameter is present I'd assert that the kernel should do some sort of sane behavior and that we don't have to force 100% strictness if the command line parameter isn't present at all. I would also note that your assertion that the system is 100% strict under the "no command line parameter" case isn't actually true as far as I can tell. The code in mainline is a little hard to follow (for me the code after my patch is easier to follow), but you can see that even before my patch a call to iommu_set_dma_strict() could be used to make the system non-strict if no command-line parameter was passed. > Alternately (and potentially a better option?), you really should be > changing/extending dev_is_untrusted() so that it applies for any > struct device (not just PCI device) and then have this overridden in > DT (or ACPI or any firmware) to indicate a specific device is safe to > use non-strict mode on. I was really trying _not_ to do that. I believe this has been talked about several times, including at last year's Linux Plumbers conference. As far as I can tell it always ends in a shouting match w/ no forward progress. There are a bunch of problems here, namely: * Trust isn't necessarily binary. There might be peripherals that you sort-of trust, others that you really trust, and others that you don't trust at all. For the ones you sort-of trust there may be some things you trust about them and other things you don't trust about them. * The firmware isn't necessarily the best arbitrar of trust. For instance, if the company that employs me (Google) compiled their own firmware for a given peripheral device and they were convinced that the peripheral firmware couldn't be compromised any more easily than code running in the kernel itself, they might assert that the peripheral device should be "trusted". An individual Linux hacker, however, might not really trust the firmware blob that Google provides and might want the device to be "untrusted". * In the PCI subsystem I believe that "trusted" vs "untrusted" is generally associated with whether a device is soldered down onto the board or in some type of slot (the "external" concept). That's been working OK for them, I think, but I'm not convinced it'd be easy to apply everywhere. One example problem: what do you do about SD cards? The thing doing the DMA (the SDHCI controller) is certainly "internal" but the cards are "external". I'm making the argument in my series that SDHCI should be considered at least trusted enough to use non-strict DMA, but it's still technically "external" and you wouldn't necessarily, for instance, trust the filesystem structure not to be crafted in a malicious way so as to exploit the kernel. > What you are trying to capture (if the device > safe enough) really isn't a function of the DMA device's driver, but a > function of the DMA device. It's a function of the DMA device, but the entity in the kernel with the most knowledge about this is the device's driver. The driver also has the best ability to make informed decisions, perhaps looking at the device's properties (like the "non-removable" one for SD/MMC) to help make decisions without us having to create a new property to describe trust and then argue about who sets it and when. -Doug
Hi, On Mon, Jun 21, 2021 at 7:05 PM Lu Baolu <baolu.lu@linux.intel.com> wrote: > > On 6/22/21 7:52 AM, Douglas Anderson wrote: > > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) > > > > static int iommu_group_alloc_default_domain(struct bus_type *bus, > > struct iommu_group *group, > > - unsigned int type) > > + unsigned int type, > > + struct device *dev) > > { > > struct iommu_domain *dom; > > > > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, > > if (!dom) > > return -ENOMEM; > > > > + /* Save the strictness requests from the device */ > > + if (dev && type == IOMMU_DOMAIN_DMA) { > > + dom->request_non_strict = dev->request_non_strict_iommu; > > + dom->force_strict = dev->force_strict_iommu; > > + } > > + > > An iommu default domain might be used by multiple devices which might > have different "strict" attributions. Then who could override who? My gut instinct would be that if multiple devices were part of a given domain that it would be combined like this: 1. Any device that requests strict makes the domain strict force strict. 2. To request non-strict all of the devices in the domain would have to request non-strict. To do that I'd have to change my patchset obviously, but I don't think it should be hard. We can just keep a count of devices and a count of the strict vs. non-strict requests? If there are no other blockers I'll try to do that in my v2. -Doug
On Mon, Jun 21, 2021 at 4:53 PM Douglas Anderson <dianders@chromium.org> wrote: > > In the patch ("drivers: base: Add bits to struct device to control > iommu strictness") we add the ability for devices to tell us about > their IOMMU strictness requirements. Let's now take that into account > in the IOMMU layer. > > A few notes here: > * Presumably this is always how iommu_get_dma_strict() was intended to > behave. Had this not been the intention then it never would have > taken a domain as a parameter. > * The iommu_set_dma_strict() feels awfully non-symmetric now. That > function sets the _default_ strictness globally in the system > whereas iommu_get_dma_strict() returns the value for a given domain > (falling back to the default). Presumably, at least, the fact that > iommu_set_dma_strict() doesn't take a domain makes this obvious. > > The function iommu_get_dma_strict() should now make it super obvious > where strictness comes from and who overides who. Though the function > changed a bunch to make the logic clearer, the only two new rules > should be: > * Devices can force strictness for themselves, overriding the cmdline > "iommu.strict=0" or a call to iommu_set_dma_strict(false)). > * Devices can request non-strictness for themselves, assuming there > was no cmdline "iommu.strict=1" or a call to > iommu_set_dma_strict(true). Along the same lines, I believe a platform (device tree / ACPI) should also be able to have a say in this. I assume in your proposal, a platform would expose a property in device tree which the device driver would need to parse and then use it to set these bits in the "struct device"? Thanks, Rajat > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > drivers/iommu/iommu.c | 56 +++++++++++++++++++++++++++++++++---------- > include/linux/iommu.h | 2 ++ > 2 files changed, 45 insertions(+), 13 deletions(-) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 808ab70d5df5..0c84a4c06110 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -28,8 +28,19 @@ > static struct kset *iommu_group_kset; > static DEFINE_IDA(iommu_group_ida); > > +enum iommu_strictness { > + IOMMU_DEFAULT_STRICTNESS = -1, > + IOMMU_NOT_STRICT = 0, > + IOMMU_STRICT = 1, > +}; > +static inline enum iommu_strictness bool_to_strictness(bool strictness) > +{ > + return (enum iommu_strictness)strictness; > +} > + > static unsigned int iommu_def_domain_type __read_mostly; > -static bool iommu_dma_strict __read_mostly = true; > +static enum iommu_strictness cmdline_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > +static enum iommu_strictness driver_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; > static u32 iommu_cmd_line __read_mostly; > > struct iommu_group { > @@ -69,7 +80,6 @@ static const char * const iommu_group_resv_type_string[] = { > }; > > #define IOMMU_CMD_LINE_DMA_API BIT(0) > -#define IOMMU_CMD_LINE_STRICT BIT(1) > > static int iommu_alloc_default_domain(struct iommu_group *group, > struct device *dev); > @@ -336,25 +346,38 @@ early_param("iommu.passthrough", iommu_set_def_domain_type); > > static int __init iommu_dma_setup(char *str) > { > - int ret = kstrtobool(str, &iommu_dma_strict); > + bool strict; > + int ret = kstrtobool(str, &strict); > > if (!ret) > - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; > + cmdline_dma_strict = bool_to_strictness(strict); > return ret; > } > early_param("iommu.strict", iommu_dma_setup); > > void iommu_set_dma_strict(bool strict) > { > - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) > - iommu_dma_strict = strict; > + /* A driver can request strictness but not the other way around */ > + if (driver_dma_strict != IOMMU_STRICT) > + driver_dma_strict = bool_to_strictness(strict); > } > > bool iommu_get_dma_strict(struct iommu_domain *domain) > { > - /* only allow lazy flushing for DMA domains */ > - if (domain->type == IOMMU_DOMAIN_DMA) > - return iommu_dma_strict; > + /* Non-DMA domains or anyone forcing it to strict makes it strict */ > + if (domain->type != IOMMU_DOMAIN_DMA || > + cmdline_dma_strict == IOMMU_STRICT || > + driver_dma_strict == IOMMU_STRICT || > + domain->force_strict) > + return true; > + > + /* Anyone requesting non-strict (if no forces) makes it non-strict */ > + if (cmdline_dma_strict == IOMMU_NOT_STRICT || > + driver_dma_strict == IOMMU_NOT_STRICT || > + domain->request_non_strict) > + return false; > + > + /* Nobody said anything, so it's strict by default */ > return true; > } > EXPORT_SYMBOL_GPL(iommu_get_dma_strict); > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) > > static int iommu_group_alloc_default_domain(struct bus_type *bus, > struct iommu_group *group, > - unsigned int type) > + unsigned int type, > + struct device *dev) > { > struct iommu_domain *dom; > > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, > if (!dom) > return -ENOMEM; > > + /* Save the strictness requests from the device */ > + if (dev && type == IOMMU_DOMAIN_DMA) { > + dom->request_non_strict = dev->request_non_strict_iommu; > + dom->force_strict = dev->force_strict_iommu; > + } > + > group->default_domain = dom; > if (!group->domain) > group->domain = dom; > @@ -1550,7 +1580,7 @@ static int iommu_alloc_default_domain(struct iommu_group *group, > > type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type; > > - return iommu_group_alloc_default_domain(dev->bus, group, type); > + return iommu_group_alloc_default_domain(dev->bus, group, type, dev); > } > > /** > @@ -1721,7 +1751,7 @@ static void probe_alloc_default_domain(struct bus_type *bus, > if (!gtype.type) > gtype.type = iommu_def_domain_type; > > - iommu_group_alloc_default_domain(bus, group, gtype.type); > + iommu_group_alloc_default_domain(bus, group, gtype.type, NULL); > > } > > @@ -3130,7 +3160,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group, > } > > /* Sets group->default_domain to the newly allocated domain */ > - ret = iommu_group_alloc_default_domain(dev->bus, group, type); > + ret = iommu_group_alloc_default_domain(dev->bus, group, type, dev); > if (ret) > goto out; > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 32d448050bf7..0bddef77f415 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -81,6 +81,8 @@ struct iommu_domain_geometry { > > struct iommu_domain { > unsigned type; > + bool force_strict:1; > + bool request_non_strict:1; > const struct iommu_ops *ops; > unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */ > iommu_fault_handler_t handler; > -- > 2.32.0.288.g62a8d224e6-goog >
Hi, On Tue, Jun 22, 2021 at 11:45 AM Rajat Jain <rajatja@google.com> wrote: > > On Mon, Jun 21, 2021 at 4:53 PM Douglas Anderson <dianders@chromium.org> wrote: > > > > In the patch ("drivers: base: Add bits to struct device to control > > iommu strictness") we add the ability for devices to tell us about > > their IOMMU strictness requirements. Let's now take that into account > > in the IOMMU layer. > > > > A few notes here: > > * Presumably this is always how iommu_get_dma_strict() was intended to > > behave. Had this not been the intention then it never would have > > taken a domain as a parameter. > > * The iommu_set_dma_strict() feels awfully non-symmetric now. That > > function sets the _default_ strictness globally in the system > > whereas iommu_get_dma_strict() returns the value for a given domain > > (falling back to the default). Presumably, at least, the fact that > > iommu_set_dma_strict() doesn't take a domain makes this obvious. > > > > The function iommu_get_dma_strict() should now make it super obvious > > where strictness comes from and who overides who. Though the function > > changed a bunch to make the logic clearer, the only two new rules > > should be: > > * Devices can force strictness for themselves, overriding the cmdline > > "iommu.strict=0" or a call to iommu_set_dma_strict(false)). > > * Devices can request non-strictness for themselves, assuming there > > was no cmdline "iommu.strict=1" or a call to > > iommu_set_dma_strict(true). > > Along the same lines, I believe a platform (device tree / ACPI) should > also be able to have a say in this. I assume in your proposal, a > platform would expose a property in device tree which the device > driver would need to parse and then use it to set these bits in the > "struct device"? Nothing would prevent creating a device tree or ACPI property that caused either "force-strict" or "request-non-strict" from being set if everyone agrees that it's a good idea. I wouldn't reject the idea myself, but I do worry that we'd devolve into the usual bikeshed for exactly how this should look. I talked about this a bit in my response to Saravana, but basically: * If there was some generic property, would we call it "untrusted", "external", or something else? * How do you describe "trust" in a generic "objective" way? It's not really boolean and trying to describe exactly how trustworthy something should be considered is hard. * At least for the device tree there's a general requirement that it describes the hardware and not so much how the software should configure the hardware. As I understand it there is _some_ leeway here where it's OK to describe how the hardware was designed for the OS to configure it, but it's a pretty high bar and a hard sell. In general the device tree isn't supposed to be used to describe "policy". In other words: if one OS might decide on one setting and another OS on another then it doesn't really belong in the device tree. * In general the kernel is also not really supposed to have policy hardcoded in either, though it feels like we can get away with having a good default/sane policy and allowing overriding the policy with command line parameters (like iommu.strict). In the case where something has to be configured at bootup there's not many ways to do better. tl;dr: I have no plans to try to make an overarching property, but my patch series does allow subsystems to come up with and easily implement their own rules as it makes sense. While this might seem hodgepodge I prefer to see it as "flexible" since I'm not convinced that we're going to be able to come up with an overarching trust framework. -Doug
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 808ab70d5df5..0c84a4c06110 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -28,8 +28,19 @@ static struct kset *iommu_group_kset; static DEFINE_IDA(iommu_group_ida); +enum iommu_strictness { + IOMMU_DEFAULT_STRICTNESS = -1, + IOMMU_NOT_STRICT = 0, + IOMMU_STRICT = 1, +}; +static inline enum iommu_strictness bool_to_strictness(bool strictness) +{ + return (enum iommu_strictness)strictness; +} + static unsigned int iommu_def_domain_type __read_mostly; -static bool iommu_dma_strict __read_mostly = true; +static enum iommu_strictness cmdline_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; +static enum iommu_strictness driver_dma_strict __read_mostly = IOMMU_DEFAULT_STRICTNESS; static u32 iommu_cmd_line __read_mostly; struct iommu_group { @@ -69,7 +80,6 @@ static const char * const iommu_group_resv_type_string[] = { }; #define IOMMU_CMD_LINE_DMA_API BIT(0) -#define IOMMU_CMD_LINE_STRICT BIT(1) static int iommu_alloc_default_domain(struct iommu_group *group, struct device *dev); @@ -336,25 +346,38 @@ early_param("iommu.passthrough", iommu_set_def_domain_type); static int __init iommu_dma_setup(char *str) { - int ret = kstrtobool(str, &iommu_dma_strict); + bool strict; + int ret = kstrtobool(str, &strict); if (!ret) - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; + cmdline_dma_strict = bool_to_strictness(strict); return ret; } early_param("iommu.strict", iommu_dma_setup); void iommu_set_dma_strict(bool strict) { - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) - iommu_dma_strict = strict; + /* A driver can request strictness but not the other way around */ + if (driver_dma_strict != IOMMU_STRICT) + driver_dma_strict = bool_to_strictness(strict); } bool iommu_get_dma_strict(struct iommu_domain *domain) { - /* only allow lazy flushing for DMA domains */ - if (domain->type == IOMMU_DOMAIN_DMA) - return iommu_dma_strict; + /* Non-DMA domains or anyone forcing it to strict makes it strict */ + if (domain->type != IOMMU_DOMAIN_DMA || + cmdline_dma_strict == IOMMU_STRICT || + driver_dma_strict == IOMMU_STRICT || + domain->force_strict) + return true; + + /* Anyone requesting non-strict (if no forces) makes it non-strict */ + if (cmdline_dma_strict == IOMMU_NOT_STRICT || + driver_dma_strict == IOMMU_NOT_STRICT || + domain->request_non_strict) + return false; + + /* Nobody said anything, so it's strict by default */ return true; } EXPORT_SYMBOL_GPL(iommu_get_dma_strict); @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev) static int iommu_group_alloc_default_domain(struct bus_type *bus, struct iommu_group *group, - unsigned int type) + unsigned int type, + struct device *dev) { struct iommu_domain *dom; @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus, if (!dom) return -ENOMEM; + /* Save the strictness requests from the device */ + if (dev && type == IOMMU_DOMAIN_DMA) { + dom->request_non_strict = dev->request_non_strict_iommu; + dom->force_strict = dev->force_strict_iommu; + } + group->default_domain = dom; if (!group->domain) group->domain = dom; @@ -1550,7 +1580,7 @@ static int iommu_alloc_default_domain(struct iommu_group *group, type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type; - return iommu_group_alloc_default_domain(dev->bus, group, type); + return iommu_group_alloc_default_domain(dev->bus, group, type, dev); } /** @@ -1721,7 +1751,7 @@ static void probe_alloc_default_domain(struct bus_type *bus, if (!gtype.type) gtype.type = iommu_def_domain_type; - iommu_group_alloc_default_domain(bus, group, gtype.type); + iommu_group_alloc_default_domain(bus, group, gtype.type, NULL); } @@ -3130,7 +3160,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group, } /* Sets group->default_domain to the newly allocated domain */ - ret = iommu_group_alloc_default_domain(dev->bus, group, type); + ret = iommu_group_alloc_default_domain(dev->bus, group, type, dev); if (ret) goto out; diff --git a/include/linux/iommu.h b/include/linux/iommu.h index 32d448050bf7..0bddef77f415 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -81,6 +81,8 @@ struct iommu_domain_geometry { struct iommu_domain { unsigned type; + bool force_strict:1; + bool request_non_strict:1; const struct iommu_ops *ops; unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */ iommu_fault_handler_t handler;
In the patch ("drivers: base: Add bits to struct device to control iommu strictness") we add the ability for devices to tell us about their IOMMU strictness requirements. Let's now take that into account in the IOMMU layer. A few notes here: * Presumably this is always how iommu_get_dma_strict() was intended to behave. Had this not been the intention then it never would have taken a domain as a parameter. * The iommu_set_dma_strict() feels awfully non-symmetric now. That function sets the _default_ strictness globally in the system whereas iommu_get_dma_strict() returns the value for a given domain (falling back to the default). Presumably, at least, the fact that iommu_set_dma_strict() doesn't take a domain makes this obvious. The function iommu_get_dma_strict() should now make it super obvious where strictness comes from and who overides who. Though the function changed a bunch to make the logic clearer, the only two new rules should be: * Devices can force strictness for themselves, overriding the cmdline "iommu.strict=0" or a call to iommu_set_dma_strict(false)). * Devices can request non-strictness for themselves, assuming there was no cmdline "iommu.strict=1" or a call to iommu_set_dma_strict(true). Signed-off-by: Douglas Anderson <dianders@chromium.org> --- drivers/iommu/iommu.c | 56 +++++++++++++++++++++++++++++++++---------- include/linux/iommu.h | 2 ++ 2 files changed, 45 insertions(+), 13 deletions(-)