| Message ID | 20201214165617.28685-1-akrowiak@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated | expand |
On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote: > The vfio_ap device driver registers a group notifier with VFIO when the > file descriptor for a VFIO mediated device for a KVM guest is opened to > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > event). When the KVM pointer is set, the vfio_ap driver takes the > following actions: > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > of the mediated device. > 2. Calls the kvm_get_kvm() function to increment its reference counter. > 3. Sets the function pointer to the function that handles interception of > the instruction that enables/disables interrupt processing. > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > the guest. > > In order to avoid memory leaks, when the notifier is called to receive > notification that the KVM pointer has been set to NULL, the vfio_ap device > driver should reverse the actions taken when the KVM pointer was set. > > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > --- > drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > 1 file changed, 20 insertions(+), 9 deletions(-) <formletter> This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly. </formletter>
On 12/14/20 12:07 PM, Greg KH wrote: > On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote: >> The vfio_ap device driver registers a group notifier with VFIO when the >> file descriptor for a VFIO mediated device for a KVM guest is opened to >> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM >> event). When the KVM pointer is set, the vfio_ap driver takes the >> following actions: >> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state >> of the mediated device. >> 2. Calls the kvm_get_kvm() function to increment its reference counter. >> 3. Sets the function pointer to the function that handles interception of >> the instruction that enables/disables interrupt processing. >> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to >> the guest. >> >> In order to avoid memory leaks, when the notifier is called to receive >> notification that the KVM pointer has been set to NULL, the vfio_ap device >> driver should reverse the actions taken when the KVM pointer was set. >> >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >> --- >> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- >> 1 file changed, 20 insertions(+), 9 deletions(-) > <formletter> > > This is not the correct way to submit patches for inclusion in the > stable kernel tree. Please read: > https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html > for how to do this properly. > > </formletter> I read the document on the correct way to submit patches for inclusion in the stable kernel. I apologize for my ignorance, but I don't see the problem. Can you help me out here? Does a patch that fixes a memory leak not qualify or is it something else?
On 12/14/20 2:43 PM, Greg KH wrote: > On Mon, Dec 14, 2020 at 02:39:17PM -0500, Tony Krowiak wrote: >> >> On 12/14/20 12:07 PM, Greg KH wrote: >>> On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote: >>>> The vfio_ap device driver registers a group notifier with VFIO when the >>>> file descriptor for a VFIO mediated device for a KVM guest is opened to >>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM >>>> event). When the KVM pointer is set, the vfio_ap driver takes the >>>> following actions: >>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state >>>> of the mediated device. >>>> 2. Calls the kvm_get_kvm() function to increment its reference counter. >>>> 3. Sets the function pointer to the function that handles interception of >>>> the instruction that enables/disables interrupt processing. >>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to >>>> the guest. >>>> >>>> In order to avoid memory leaks, when the notifier is called to receive >>>> notification that the KVM pointer has been set to NULL, the vfio_ap device >>>> driver should reverse the actions taken when the KVM pointer was set. >>>> >>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >>>> --- >>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- >>>> 1 file changed, 20 insertions(+), 9 deletions(-) >>> <formletter> >>> >>> This is not the correct way to submit patches for inclusion in the >>> stable kernel tree. Please read: >>> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html >>> for how to do this properly. >>> >>> </formletter> >> I read the document on the correct way to submit patches for inclusion in >> the stable kernel. I apologize for my ignorance, but I don't see the >> problem. Can you help me out here? Does a patch that fixes a memory leak >> not qualify or is it something else? > You forgot to put "Cc: stable..." in the signed-off-by area. > > thanks, Option 1, I must be blind. thanks > > greg k-h
On Mon, 14 Dec 2020 11:56:17 -0500 Tony Krowiak <akrowiak@linux.ibm.com> wrote: > The vfio_ap device driver registers a group notifier with VFIO when the > file descriptor for a VFIO mediated device for a KVM guest is opened to > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > event). When the KVM pointer is set, the vfio_ap driver takes the > following actions: > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > of the mediated device. > 2. Calls the kvm_get_kvm() function to increment its reference counter. > 3. Sets the function pointer to the function that handles interception of > the instruction that enables/disables interrupt processing. > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > the guest. > > In order to avoid memory leaks, when the notifier is called to receive > notification that the KVM pointer has been set to NULL, the vfio_ap device > driver should reverse the actions taken when the KVM pointer was set. > > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > --- > drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > 1 file changed, 20 insertions(+), 9 deletions(-) > > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c > index e0bde8518745..cd22e85588e1 100644 > --- a/drivers/s390/crypto/vfio_ap_ops.c > +++ b/drivers/s390/crypto/vfio_ap_ops.c > @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > { > struct ap_matrix_mdev *m; > > - mutex_lock(&matrix_dev->lock); > - > list_for_each_entry(m, &matrix_dev->mdev_list, node) { > if ((m != matrix_mdev) && (m->kvm == kvm)) { > mutex_unlock(&matrix_dev->lock); > @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > matrix_mdev->kvm = kvm; > kvm_get_kvm(kvm); > kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; > - mutex_unlock(&matrix_dev->lock); > > return 0; > } > @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, > return NOTIFY_DONE; > } > > +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) > +{ > + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); > + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; This patch LGTM. The only concern I have with it is whether a different cpu is guaranteed to observe the above assignment as an atomic operation. I think we didn't finish this discussion at v1, or did we? Regards, Halil > + vfio_ap_mdev_reset_queues(matrix_mdev->mdev); > + kvm_put_kvm(matrix_mdev->kvm); > + matrix_mdev->kvm = NULL; > +} > + > static int vfio_ap_mdev_group_notifier(struct notifier_block *nb, > unsigned long action, void *data) > { > - int ret; > + int ret, notify_rc = NOTIFY_DONE; > struct ap_matrix_mdev *matrix_mdev; > > if (action != VFIO_GROUP_NOTIFY_SET_KVM) > return NOTIFY_OK; > > matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier); > + mutex_lock(&matrix_dev->lock); > > if (!data) { > - matrix_mdev->kvm = NULL; > - return NOTIFY_OK; > + if (matrix_mdev->kvm) > + vfio_ap_mdev_unset_kvm(matrix_mdev); > + notify_rc = NOTIFY_OK; > + goto notify_done; > } > > ret = vfio_ap_mdev_set_kvm(matrix_mdev, data); > if (ret) > - return NOTIFY_DONE; > + goto notify_done; > > /* If there is no CRYCB pointer, then we can't copy the masks */ > if (!matrix_mdev->kvm->arch.crypto.crycbd) > - return NOTIFY_DONE; > + goto notify_done; > > kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm, > matrix_mdev->matrix.aqm, > matrix_mdev->matrix.adm); > > - return NOTIFY_OK; > +notify_done: > + mutex_unlock(&matrix_dev->lock); > + return notify_rc; > } > > static void vfio_ap_irq_disable_apqn(int apqn)
On Mon, 14 Dec 2020 11:56:17 -0500 Tony Krowiak <akrowiak@linux.ibm.com> wrote: > The vfio_ap device driver registers a group notifier with VFIO when the > file descriptor for a VFIO mediated device for a KVM guest is opened to > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > event). When the KVM pointer is set, the vfio_ap driver takes the > following actions: > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > of the mediated device. > 2. Calls the kvm_get_kvm() function to increment its reference counter. > 3. Sets the function pointer to the function that handles interception of > the instruction that enables/disables interrupt processing. > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > the guest. > > In order to avoid memory leaks, when the notifier is called to receive > notification that the KVM pointer has been set to NULL, the vfio_ap device > driver should reverse the actions taken when the KVM pointer was set. > > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > --- > drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > 1 file changed, 20 insertions(+), 9 deletions(-) Reviewed-by: Cornelia Huck <cohuck@redhat.com>
On 15.12.20 11:57, Halil Pasic wrote: > On Mon, 14 Dec 2020 11:56:17 -0500 > Tony Krowiak <akrowiak@linux.ibm.com> wrote: > >> The vfio_ap device driver registers a group notifier with VFIO when the >> file descriptor for a VFIO mediated device for a KVM guest is opened to >> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM >> event). When the KVM pointer is set, the vfio_ap driver takes the >> following actions: >> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state >> of the mediated device. >> 2. Calls the kvm_get_kvm() function to increment its reference counter. >> 3. Sets the function pointer to the function that handles interception of >> the instruction that enables/disables interrupt processing. >> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to >> the guest. >> >> In order to avoid memory leaks, when the notifier is called to receive >> notification that the KVM pointer has been set to NULL, the vfio_ap device >> driver should reverse the actions taken when the KVM pointer was set. >> >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >> --- >> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- >> 1 file changed, 20 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c >> index e0bde8518745..cd22e85588e1 100644 >> --- a/drivers/s390/crypto/vfio_ap_ops.c >> +++ b/drivers/s390/crypto/vfio_ap_ops.c >> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >> { >> struct ap_matrix_mdev *m; >> >> - mutex_lock(&matrix_dev->lock); >> - >> list_for_each_entry(m, &matrix_dev->mdev_list, node) { >> if ((m != matrix_mdev) && (m->kvm == kvm)) { >> mutex_unlock(&matrix_dev->lock); >> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >> matrix_mdev->kvm = kvm; >> kvm_get_kvm(kvm); >> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; >> - mutex_unlock(&matrix_dev->lock); >> >> return 0; >> } >> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, >> return NOTIFY_DONE; >> } >> >> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >> +{ >> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > > > This patch LGTM. The only concern I have with it is whether a > different cpu is guaranteed to observe the above assignment as > an atomic operation. I think we didn't finish this discussion > at v1, or did we? You mean just this assigment: >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; should either have the old or the new value, but not halve zero halve old? Normally this should be ok (and I would consider this a compiler bug if this is split into 2 32 bit zeroes) But if you really want to be sure then we can use WRITE_ONCE. I think we take this via the s390 tree? I can add the WRITE_ONCE when applying?
On Tue, 15 Dec 2020 19:10:20 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote: > > > On 15.12.20 11:57, Halil Pasic wrote: > > On Mon, 14 Dec 2020 11:56:17 -0500 > > Tony Krowiak <akrowiak@linux.ibm.com> wrote: > > > >> The vfio_ap device driver registers a group notifier with VFIO when the > >> file descriptor for a VFIO mediated device for a KVM guest is opened to > >> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > >> event). When the KVM pointer is set, the vfio_ap driver takes the > >> following actions: > >> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > >> of the mediated device. > >> 2. Calls the kvm_get_kvm() function to increment its reference counter. > >> 3. Sets the function pointer to the function that handles interception of > >> the instruction that enables/disables interrupt processing. > >> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > >> the guest. > >> > >> In order to avoid memory leaks, when the notifier is called to receive > >> notification that the KVM pointer has been set to NULL, the vfio_ap device > >> driver should reverse the actions taken when the KVM pointer was set. > >> > >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > >> --- > >> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > >> 1 file changed, 20 insertions(+), 9 deletions(-) > >> > >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c > >> index e0bde8518745..cd22e85588e1 100644 > >> --- a/drivers/s390/crypto/vfio_ap_ops.c > >> +++ b/drivers/s390/crypto/vfio_ap_ops.c > >> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > >> { > >> struct ap_matrix_mdev *m; > >> > >> - mutex_lock(&matrix_dev->lock); > >> - > >> list_for_each_entry(m, &matrix_dev->mdev_list, node) { > >> if ((m != matrix_mdev) && (m->kvm == kvm)) { > >> mutex_unlock(&matrix_dev->lock); > >> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > >> matrix_mdev->kvm = kvm; > >> kvm_get_kvm(kvm); > >> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; > >> - mutex_unlock(&matrix_dev->lock); > >> > >> return 0; > >> } > >> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, > >> return NOTIFY_DONE; > >> } > >> > >> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) > >> +{ > >> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); > >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > > > > > > This patch LGTM. The only concern I have with it is whether a > > different cpu is guaranteed to observe the above assignment as > > an atomic operation. I think we didn't finish this discussion > > at v1, or did we? > > You mean just this assigment: > >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > should either have the old or the new value, but not halve zero halve old? > Yes that is the assignment I was referring to. Old value will work as well because kvm holds a reference to this module while in the pqap_hook. > Normally this should be ok (and I would consider this a compiler bug if > this is split into 2 32 bit zeroes) But if you really want to be sure then we > can use WRITE_ONCE. Just my curiosity: what would make this a bug? Is it the s390 elf ABI, or some gcc feature, or even the C standard? Also how exactly would WRITE_ONCE, also access via volatile help in this particular situation? I agree, if the member is properly aligned, (which it is), normally/probably we are fine on s390x (which is also a given). > I think we take this via the s390 tree? I can add the WRITE_ONCE when applying? Yes that works fine with me. Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
On 16.12.20 02:21, Halil Pasic wrote: > On Tue, 15 Dec 2020 19:10:20 +0100 > Christian Borntraeger <borntraeger@de.ibm.com> wrote: > >> >> >> On 15.12.20 11:57, Halil Pasic wrote: >>> On Mon, 14 Dec 2020 11:56:17 -0500 >>> Tony Krowiak <akrowiak@linux.ibm.com> wrote: >>> >>>> The vfio_ap device driver registers a group notifier with VFIO when the >>>> file descriptor for a VFIO mediated device for a KVM guest is opened to >>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM >>>> event). When the KVM pointer is set, the vfio_ap driver takes the >>>> following actions: >>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state >>>> of the mediated device. >>>> 2. Calls the kvm_get_kvm() function to increment its reference counter. >>>> 3. Sets the function pointer to the function that handles interception of >>>> the instruction that enables/disables interrupt processing. >>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to >>>> the guest. >>>> >>>> In order to avoid memory leaks, when the notifier is called to receive >>>> notification that the KVM pointer has been set to NULL, the vfio_ap device >>>> driver should reverse the actions taken when the KVM pointer was set. >>>> >>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >>>> --- >>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- >>>> 1 file changed, 20 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c >>>> index e0bde8518745..cd22e85588e1 100644 >>>> --- a/drivers/s390/crypto/vfio_ap_ops.c >>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c >>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >>>> { >>>> struct ap_matrix_mdev *m; >>>> >>>> - mutex_lock(&matrix_dev->lock); >>>> - >>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) { >>>> if ((m != matrix_mdev) && (m->kvm == kvm)) { >>>> mutex_unlock(&matrix_dev->lock); >>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >>>> matrix_mdev->kvm = kvm; >>>> kvm_get_kvm(kvm); >>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; >>>> - mutex_unlock(&matrix_dev->lock); >>>> >>>> return 0; >>>> } >>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, >>>> return NOTIFY_DONE; >>>> } >>>> >>>> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >>>> +{ >>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; >>> >>> >>> This patch LGTM. The only concern I have with it is whether a >>> different cpu is guaranteed to observe the above assignment as >>> an atomic operation. I think we didn't finish this discussion >>> at v1, or did we? >> >> You mean just this assigment: >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; >> should either have the old or the new value, but not halve zero halve old? >> > > Yes that is the assignment I was referring to. Old value will work as well because > kvm holds a reference to this module while in the pqap_hook. > >> Normally this should be ok (and I would consider this a compiler bug if >> this is split into 2 32 bit zeroes) But if you really want to be sure then we >> can use WRITE_ONCE. > > Just my curiosity: what would make this a bug? Is it the s390 elf ABI, > or some gcc feature, or even the C standard? Also how exactly would > WRITE_ONCE, also access via volatile help in this particular situation? I think its a tricky things and not strictly guaranteed, but there is a lot of code that relies on the atomicity of word sizes. see for example the discussion here https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/ WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation that we assume atomic access here. > > I agree, if the member is properly aligned, (which it is), > normally/probably we are fine on s390x (which is also a given). > >> I think we take this via the s390 tree? I can add the WRITE_ONCE when applying? > > Yes that works fine with me. > > Reviewed-by: Halil Pasic <pasic@linux.ibm.com> >
On Wed, 16 Dec 2020 10:58:48 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote: > On 16.12.20 02:21, Halil Pasic wrote: > > On Tue, 15 Dec 2020 19:10:20 +0100 > > Christian Borntraeger <borntraeger@de.ibm.com> wrote: > > > >> > >> > >> On 15.12.20 11:57, Halil Pasic wrote: > >>> On Mon, 14 Dec 2020 11:56:17 -0500 > >>> Tony Krowiak <akrowiak@linux.ibm.com> wrote: > >>> > >>>> The vfio_ap device driver registers a group notifier with VFIO when the > >>>> file descriptor for a VFIO mediated device for a KVM guest is opened to > >>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > >>>> event). When the KVM pointer is set, the vfio_ap driver takes the > >>>> following actions: > >>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > >>>> of the mediated device. > >>>> 2. Calls the kvm_get_kvm() function to increment its reference counter. > >>>> 3. Sets the function pointer to the function that handles interception of > >>>> the instruction that enables/disables interrupt processing. > >>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > >>>> the guest. > >>>> > >>>> In order to avoid memory leaks, when the notifier is called to receive > >>>> notification that the KVM pointer has been set to NULL, the vfio_ap device > >>>> driver should reverse the actions taken when the KVM pointer was set. > >>>> > >>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > >>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > >>>> --- > >>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > >>>> 1 file changed, 20 insertions(+), 9 deletions(-) > >>>> > >>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c > >>>> index e0bde8518745..cd22e85588e1 100644 > >>>> --- a/drivers/s390/crypto/vfio_ap_ops.c > >>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c > >>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > >>>> { > >>>> struct ap_matrix_mdev *m; > >>>> > >>>> - mutex_lock(&matrix_dev->lock); > >>>> - > >>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) { > >>>> if ((m != matrix_mdev) && (m->kvm == kvm)) { > >>>> mutex_unlock(&matrix_dev->lock); > >>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > >>>> matrix_mdev->kvm = kvm; > >>>> kvm_get_kvm(kvm); > >>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; > >>>> - mutex_unlock(&matrix_dev->lock); > >>>> > >>>> return 0; > >>>> } > >>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, > >>>> return NOTIFY_DONE; > >>>> } > >>>> > >>>> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) > >>>> +{ > >>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); > >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > >>> > >>> > >>> This patch LGTM. The only concern I have with it is whether a > >>> different cpu is guaranteed to observe the above assignment as > >>> an atomic operation. I think we didn't finish this discussion > >>> at v1, or did we? > >> > >> You mean just this assigment: > >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > >> should either have the old or the new value, but not halve zero halve old? > >> > > > > Yes that is the assignment I was referring to. Old value will work as well because > > kvm holds a reference to this module while in the pqap_hook. > > > >> Normally this should be ok (and I would consider this a compiler bug if > >> this is split into 2 32 bit zeroes) But if you really want to be sure then we > >> can use WRITE_ONCE. > > > > Just my curiosity: what would make this a bug? Is it the s390 elf ABI, > > or some gcc feature, or even the C standard? Also how exactly would > > WRITE_ONCE, also access via volatile help in this particular situation? > > I think its a tricky things and not strictly guaranteed, but there is a lot > of code that relies on the atomicity of word sizes. see for example the discussion > here > https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/ > > WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation > that we assume atomic access here. Thanks a lot! I've read it, and IMHO it seems to contradict the section https://lwn.net/Articles/793253/#Store%20Tearing a little. From there, I also learned that WRITE_ONCE (i.e. volatile access) can help, although I don't really understand why. Of course, we don't need to be portable here, as this is s390 only code. So we might be safe without anything -- I don't know. I believe, if volatile were enough (under any circumstances), the C standard wouldn't have introduced atomic types. Regards, Halil
On 12/14/20 11:56 AM, Tony Krowiak wrote: > The vfio_ap device driver registers a group notifier with VFIO when the > file descriptor for a VFIO mediated device for a KVM guest is opened to > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM > event). When the KVM pointer is set, the vfio_ap driver takes the > following actions: > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state > of the mediated device. > 2. Calls the kvm_get_kvm() function to increment its reference counter. > 3. Sets the function pointer to the function that handles interception of > the instruction that enables/disables interrupt processing. > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to > the guest. > > In order to avoid memory leaks, when the notifier is called to receive > notification that the KVM pointer has been set to NULL, the vfio_ap device > driver should reverse the actions taken when the KVM pointer was set. > > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> > --- > drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- > 1 file changed, 20 insertions(+), 9 deletions(-) > > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c > index e0bde8518745..cd22e85588e1 100644 > --- a/drivers/s390/crypto/vfio_ap_ops.c > +++ b/drivers/s390/crypto/vfio_ap_ops.c > @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > { > struct ap_matrix_mdev *m; > > - mutex_lock(&matrix_dev->lock); > - > list_for_each_entry(m, &matrix_dev->mdev_list, node) { > if ((m != matrix_mdev) && (m->kvm == kvm)) { > mutex_unlock(&matrix_dev->lock); This unlock needs to be removed. > @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, > matrix_mdev->kvm = kvm; > kvm_get_kvm(kvm); > kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; > - mutex_unlock(&matrix_dev->lock); > > return 0; > } > @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, > return NOTIFY_DONE; > } > > +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) > +{ > + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); > + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > + vfio_ap_mdev_reset_queues(matrix_mdev->mdev); > + kvm_put_kvm(matrix_mdev->kvm); > + matrix_mdev->kvm = NULL; > +} > + > static int vfio_ap_mdev_group_notifier(struct notifier_block *nb, > unsigned long action, void *data) > { > - int ret; > + int ret, notify_rc = NOTIFY_DONE; > struct ap_matrix_mdev *matrix_mdev; > > if (action != VFIO_GROUP_NOTIFY_SET_KVM) > return NOTIFY_OK; > > matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier); > + mutex_lock(&matrix_dev->lock); > > if (!data) { > - matrix_mdev->kvm = NULL; > - return NOTIFY_OK; > + if (matrix_mdev->kvm) > + vfio_ap_mdev_unset_kvm(matrix_mdev); > + notify_rc = NOTIFY_OK; > + goto notify_done; > } > > ret = vfio_ap_mdev_set_kvm(matrix_mdev, data); > if (ret) > - return NOTIFY_DONE; > + goto notify_done; > > /* If there is no CRYCB pointer, then we can't copy the masks */ > if (!matrix_mdev->kvm->arch.crypto.crycbd) > - return NOTIFY_DONE; > + goto notify_done; > > kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm, > matrix_mdev->matrix.aqm, > matrix_mdev->matrix.adm); > > - return NOTIFY_OK; > +notify_done: > + mutex_unlock(&matrix_dev->lock); > + return notify_rc; > } > > static void vfio_ap_irq_disable_apqn(int apqn)
diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index e0bde8518745..cd22e85588e1 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, { struct ap_matrix_mdev *m; - mutex_lock(&matrix_dev->lock); - list_for_each_entry(m, &matrix_dev->mdev_list, node) { if ((m != matrix_mdev) && (m->kvm == kvm)) { mutex_unlock(&matrix_dev->lock); @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, matrix_mdev->kvm = kvm; kvm_get_kvm(kvm); kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; - mutex_unlock(&matrix_dev->lock); return 0; } @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, return NOTIFY_DONE; } +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) +{ + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; + vfio_ap_mdev_reset_queues(matrix_mdev->mdev); + kvm_put_kvm(matrix_mdev->kvm); + matrix_mdev->kvm = NULL; +} + static int vfio_ap_mdev_group_notifier(struct notifier_block *nb, unsigned long action, void *data) { - int ret; + int ret, notify_rc = NOTIFY_DONE; struct ap_matrix_mdev *matrix_mdev; if (action != VFIO_GROUP_NOTIFY_SET_KVM) return NOTIFY_OK; matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier); + mutex_lock(&matrix_dev->lock); if (!data) { - matrix_mdev->kvm = NULL; - return NOTIFY_OK; + if (matrix_mdev->kvm) + vfio_ap_mdev_unset_kvm(matrix_mdev); + notify_rc = NOTIFY_OK; + goto notify_done; } ret = vfio_ap_mdev_set_kvm(matrix_mdev, data); if (ret) - return NOTIFY_DONE; + goto notify_done; /* If there is no CRYCB pointer, then we can't copy the masks */ if (!matrix_mdev->kvm->arch.crypto.crycbd) - return NOTIFY_DONE; + goto notify_done; kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm, matrix_mdev->matrix.aqm, matrix_mdev->matrix.adm); - return NOTIFY_OK; +notify_done: + mutex_unlock(&matrix_dev->lock); + return notify_rc; } static void vfio_ap_irq_disable_apqn(int apqn)
The vfio_ap device driver registers a group notifier with VFIO when the file descriptor for a VFIO mediated device for a KVM guest is opened to receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM event). When the KVM pointer is set, the vfio_ap driver takes the following actions: 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state of the mediated device. 2. Calls the kvm_get_kvm() function to increment its reference counter. 3. Sets the function pointer to the function that handles interception of the instruction that enables/disables interrupt processing. 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to the guest. In order to avoid memory leaks, when the notifier is called to receive notification that the KVM pointer has been set to NULL, the vfio_ap device driver should reverse the actions taken when the KVM pointer was set. Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> --- drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-)