| Message ID | 20230517162817.8538-4-wyes.karny@amd.com (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | cpufreq/amd-pstate: Fix null pointer dereference when frequency invariance is disabled | expand |
On Wed, May 17, 2023 at 6:30 PM Wyes Karny <wyes.karny@amd.com> wrote: > > If fast_switch_possible flag is set by the scaling driver, the governor > is free to select fast_switch function even if adjust_perf is set. Some > scaling drivers which use adjust_perf don't set fast_switch thinking > that the governor would never fall back to fast_switch. But the governor > can fall back to fast_switch even in runtime if frequency invariance is > disabled due to some reason. This could crash the kernel if the driver > didn't set the fast_switch function pointer. > > Therefore, return failure in cpufreq_online function if fast_switch is > not set and fast_switch_possible is set. > > Signed-off-by: Wyes Karny <wyes.karny@amd.com> > --- > drivers/cpufreq/cpufreq.c | 5 +++++ > include/linux/cpufreq.h | 4 +++- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 6b52ebe5a890..7835ba4fa34c 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1376,6 +1376,11 @@ static int cpufreq_online(unsigned int cpu) > goto out_free_policy; > } > > + if (policy->fast_switch_possible && !cpufreq_driver->fast_switch) { > + pr_err("fast_switch_possible is enabled but fast_switch callback is not set\n"); > + ret = -EINVAL; > + goto out_destroy_policy; > + } The driver registration can fail if the driver has ->adjust_perf without ->fast_switch. Then the check above would not be necessary any more. > /* > * The initialization has succeeded and the policy is online. > * If there is a problem with its frequency table, take it > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h > index 26e2eb399484..8cdf77bb3bc1 100644 > --- a/include/linux/cpufreq.h > +++ b/include/linux/cpufreq.h > @@ -340,7 +340,9 @@ struct cpufreq_driver { > /* > * ->fast_switch() replacement for drivers that use an internal > * representation of performance levels and can pass hints other than > - * the target performance level to the hardware. > + * the target performance level to the hardware. If driver is setting this, > + * then it needs to set fast_switch also. Because in certain scenario scale > + * invariance could be disabled and governor can switch back to fast_switch. I would say something like "This can only be set if ->fast_switch is set too, because in those cases (under specific conditions) scale invariance can be disabled, which causes the schedutil governor to fall back to the latter." > */ > void (*adjust_perf)(unsigned int cpu, > unsigned long min_perf, > -- > 2.34.1 >
Hi Rafael, On 24 May 19:44, Rafael J. Wysocki wrote: > On Wed, May 17, 2023 at 6:30 PM Wyes Karny <wyes.karny@amd.com> wrote: > > > > If fast_switch_possible flag is set by the scaling driver, the governor > > is free to select fast_switch function even if adjust_perf is set. Some > > scaling drivers which use adjust_perf don't set fast_switch thinking > > that the governor would never fall back to fast_switch. But the governor > > can fall back to fast_switch even in runtime if frequency invariance is > > disabled due to some reason. This could crash the kernel if the driver > > didn't set the fast_switch function pointer. > > > > Therefore, return failure in cpufreq_online function if fast_switch is > > not set and fast_switch_possible is set. > > > > Signed-off-by: Wyes Karny <wyes.karny@amd.com> > > --- > > drivers/cpufreq/cpufreq.c | 5 +++++ > > include/linux/cpufreq.h | 4 +++- > > 2 files changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > index 6b52ebe5a890..7835ba4fa34c 100644 > > --- a/drivers/cpufreq/cpufreq.c > > +++ b/drivers/cpufreq/cpufreq.c > > @@ -1376,6 +1376,11 @@ static int cpufreq_online(unsigned int cpu) > > goto out_free_policy; > > } > > > > + if (policy->fast_switch_possible && !cpufreq_driver->fast_switch) { > > + pr_err("fast_switch_possible is enabled but fast_switch callback is not set\n"); > > + ret = -EINVAL; > > + goto out_destroy_policy; > > + } > > The driver registration can fail if the driver has ->adjust_perf > without ->fast_switch. Then the check above would not be necessary > any more. Sure. Will do that. > > > /* > > * The initialization has succeeded and the policy is online. > > * If there is a problem with its frequency table, take it > > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h > > index 26e2eb399484..8cdf77bb3bc1 100644 > > --- a/include/linux/cpufreq.h > > +++ b/include/linux/cpufreq.h > > @@ -340,7 +340,9 @@ struct cpufreq_driver { > > /* > > * ->fast_switch() replacement for drivers that use an internal > > * representation of performance levels and can pass hints other than > > - * the target performance level to the hardware. > > + * the target performance level to the hardware. If driver is setting this, > > + * then it needs to set fast_switch also. Because in certain scenario scale > > + * invariance could be disabled and governor can switch back to fast_switch. > > I would say something like "This can only be set if ->fast_switch is > set too, because in those cases (under specific conditions) scale > invariance can be disabled, which causes the schedutil governor to > fall back to the latter." Sure. Will update and send the updated patch in-reply-to this. Thanks & Regards, Wyes > > > */ > > void (*adjust_perf)(unsigned int cpu, > > unsigned long min_perf, > > -- > > 2.34.1 > >
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 6b52ebe5a890..7835ba4fa34c 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1376,6 +1376,11 @@ static int cpufreq_online(unsigned int cpu) goto out_free_policy; } + if (policy->fast_switch_possible && !cpufreq_driver->fast_switch) { + pr_err("fast_switch_possible is enabled but fast_switch callback is not set\n"); + ret = -EINVAL; + goto out_destroy_policy; + } /* * The initialization has succeeded and the policy is online. * If there is a problem with its frequency table, take it diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 26e2eb399484..8cdf77bb3bc1 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -340,7 +340,9 @@ struct cpufreq_driver { /* * ->fast_switch() replacement for drivers that use an internal * representation of performance levels and can pass hints other than - * the target performance level to the hardware. + * the target performance level to the hardware. If driver is setting this, + * then it needs to set fast_switch also. Because in certain scenario scale + * invariance could be disabled and governor can switch back to fast_switch. */ void (*adjust_perf)(unsigned int cpu, unsigned long min_perf,
If fast_switch_possible flag is set by the scaling driver, the governor is free to select fast_switch function even if adjust_perf is set. Some scaling drivers which use adjust_perf don't set fast_switch thinking that the governor would never fall back to fast_switch. But the governor can fall back to fast_switch even in runtime if frequency invariance is disabled due to some reason. This could crash the kernel if the driver didn't set the fast_switch function pointer. Therefore, return failure in cpufreq_online function if fast_switch is not set and fast_switch_possible is set. Signed-off-by: Wyes Karny <wyes.karny@amd.com> --- drivers/cpufreq/cpufreq.c | 5 +++++ include/linux/cpufreq.h | 4 +++- 2 files changed, 8 insertions(+), 1 deletion(-)