mbox series

[0/2] xen: fix illegal rtc device usage of pv guests

Message ID 20210903084937.19392-1-jgross@suse.com
Headers show
Series xen: fix illegal rtc device usage of pv guests | expand

Message

Juergen Gross Sept. 3, 2021, 8:49 a.m. UTC 
A recent change in mc146818_get_time() resulted in WARN splats when
booting a Xen PV guest.

The main reason is that there is a code path resulting in accessing a
RTC device which is not present, which has been made obvious by a
call of WARN() in this case.

This small series is fixing this issue by:

- avoiding the RTC device access from drivers/base/power/trace.c in
  cast there is no legacy RTC device available
- resetting the availability flag of a legacy RTC device for Xen PV
  guests

Juergen Gross (2):
  PM: base: power: don't try to use non-existing RTC for storing data
  xen: reset legacy rtc flag for PV domU

 arch/x86/xen/enlighten_pv.c |  7 +++++++
 drivers/base/power/trace.c  | 10 ++++++++++
 2 files changed, 17 insertions(+)

Comments

Greg Kroah-Hartman Sept. 3, 2021, 8:56 a.m. UTC | #1 
On Fri, Sep 03, 2021 at 10:49:36AM +0200, Juergen Gross wrote:
> In there is no legacy RTC device, don't try to use it for storing trace
> data across suspend/resume.
> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  drivers/base/power/trace.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/base/power/trace.c b/drivers/base/power/trace.c
> index a97f33d0c59f..b7c80849455c 100644
> --- a/drivers/base/power/trace.c
> +++ b/drivers/base/power/trace.c
> @@ -13,6 +13,7 @@
>  #include <linux/export.h>
>  #include <linux/rtc.h>
>  #include <linux/suspend.h>
> +#include <linux/init.h>
>  
>  #include <linux/mc146818rtc.h>
>  
> @@ -165,6 +166,9 @@ void generate_pm_trace(const void *tracedata, unsigned int user)
>  	const char *file = *(const char **)(tracedata + 2);
>  	unsigned int user_hash_value, file_hash_value;
>  
> +	if (!x86_platform.legacy.rtc)
> +		return 0;

Why does the driver core code here care about a platform/arch-specific
thing at all?  Did you just break all other arches?

thanks,

greg k-h
Greg Kroah-Hartman Sept. 3, 2021, 9:08 a.m. UTC | #2 
On Fri, Sep 03, 2021 at 11:01:58AM +0200, Juergen Gross wrote:
> On 03.09.21 10:56, Greg Kroah-Hartman wrote:
> > On Fri, Sep 03, 2021 at 10:49:36AM +0200, Juergen Gross wrote:
> > > In there is no legacy RTC device, don't try to use it for storing trace
> > > data across suspend/resume.
> > > 
> > > Cc: <stable@vger.kernel.org>
> > > Signed-off-by: Juergen Gross <jgross@suse.com>
> > > ---
> > >   drivers/base/power/trace.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/drivers/base/power/trace.c b/drivers/base/power/trace.c
> > > index a97f33d0c59f..b7c80849455c 100644
> > > --- a/drivers/base/power/trace.c
> > > +++ b/drivers/base/power/trace.c
> > > @@ -13,6 +13,7 @@
> > >   #include <linux/export.h>
> > >   #include <linux/rtc.h>
> > >   #include <linux/suspend.h>
> > > +#include <linux/init.h>
> > >   #include <linux/mc146818rtc.h>
> > > @@ -165,6 +166,9 @@ void generate_pm_trace(const void *tracedata, unsigned int user)
> > >   	const char *file = *(const char **)(tracedata + 2);
> > >   	unsigned int user_hash_value, file_hash_value;
> > > +	if (!x86_platform.legacy.rtc)
> > > +		return 0;
> > 
> > Why does the driver core code here care about a platform/arch-specific
> > thing at all?  Did you just break all other arches?
> 
> This file is only compiled for x86. It depends on CONFIG_PM_TRACE_RTC,
> which has a "depends on X86" attribute.

Odd, and not obvious at all :(

Ok, I'll let Rafael review this...
Juergen Gross Sept. 7, 2021, 4:18 a.m. UTC | #3 
On 06.09.21 19:07, Rafael J. Wysocki wrote:
> On Fri, Sep 3, 2021 at 11:02 AM Juergen Gross <jgross@suse.com> wrote:
>>
>> On 03.09.21 10:56, Greg Kroah-Hartman wrote:
>>> On Fri, Sep 03, 2021 at 10:49:36AM +0200, Juergen Gross wrote:
>>>> In there is no legacy RTC device, don't try to use it for storing trace
>>>> data across suspend/resume.
>>>>
>>>> Cc: <stable@vger.kernel.org>
>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>> ---
>>>>    drivers/base/power/trace.c | 10 ++++++++++
>>>>    1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/base/power/trace.c b/drivers/base/power/trace.c
>>>> index a97f33d0c59f..b7c80849455c 100644
>>>> --- a/drivers/base/power/trace.c
>>>> +++ b/drivers/base/power/trace.c
>>>> @@ -13,6 +13,7 @@
>>>>    #include <linux/export.h>
>>>>    #include <linux/rtc.h>
>>>>    #include <linux/suspend.h>
>>>> +#include <linux/init.h>
>>>>
>>>>    #include <linux/mc146818rtc.h>
>>>>
>>>> @@ -165,6 +166,9 @@ void generate_pm_trace(const void *tracedata, unsigned int user)
>>>>       const char *file = *(const char **)(tracedata + 2);
>>>>       unsigned int user_hash_value, file_hash_value;
>>>>
>>>> +    if (!x86_platform.legacy.rtc)
>>>> +            return 0;
>>>
>>> Why does the driver core code here care about a platform/arch-specific
>>> thing at all?  Did you just break all other arches?
>>
>> This file is only compiled for x86. It depends on CONFIG_PM_TRACE_RTC,
>> which has a "depends on X86" attribute.
> 
> This feature uses the CMOS RTC memory to store data, so if that memory
> is not present, it's better to avoid using it.
> 
> Please feel free to add
> 
> Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

Thanks!

> 
> to this patch or let me know if you want me to take it.
> 

No, I can take it with the other patch of this small series, thanks.


Juergen