`amd_pstate_set_epp` function uses `cppc_req_cached` and `epp` variable
to update the MSR_AMD_CPPC_REQ register for AMD MSR systems. The recent
commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable
use") changed the sequence of updating cppc_req_cached and writing the
MSR_AMD_CPPC_REQ. Therefore while switching from powersave to
performance governor and vice-versa in active mode MSR_AMD_CPPC_REQ is
set with the previous cached value. To fix this: first update the
`cppc_req_cached` variable and then call `amd_pstate_set_epp` function.
- Before commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
variable use"):
With powersave governor:
[ 1.652743] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
[ 1.652744] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
[ 1.652746] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
Changing to performance governor:
[ 300.493842] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
[ 300.493846] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
[ 300.493847] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
- After commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
variable use"):
With powersave governor:
[ 1.646037] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
[ 1.646038] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
[ 1.646042] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
Changing to performance governor:
[ 687.117401] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
[ 687.117405] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
[ 687.117419] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
- After this fix:
With powersave governor:
[ 2.525717] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
[ 2.525720] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
[ 2.525722] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
Changing to performance governor:
[ 3440.152468] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
[ 3440.152473] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
[ 3440.152474] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
Fixes: 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable use")
Signed-off-by: Wyes Karny <[email protected]>
---
drivers/cpufreq/amd-pstate.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index b8862afef4e4..45c88894fd8e 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1057,27 +1057,28 @@ static void amd_pstate_epp_init(unsigned int cpu)
cpudata->epp_policy = cpudata->policy;
- if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) {
- epp = amd_pstate_get_epp(cpudata, value);
- if (epp < 0)
- goto skip_epp;
- /* force the epp value to be zero for performance policy */
- epp = 0;
- } else {
- /* Get BIOS pre-defined epp value */
- epp = amd_pstate_get_epp(cpudata, value);
- if (epp)
- goto skip_epp;
+ /* Get BIOS pre-defined epp value */
+ epp = amd_pstate_get_epp(cpudata, value);
+ if (epp < 0) {
+ /**
+ * This return value can only be negative for shared_memory
+ * systems where EPP register read/write not supported.
+ */
+ goto skip_epp;
}
+
+ if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
+ epp = 0;
+
/* Set initial EPP value */
if (boot_cpu_has(X86_FEATURE_CPPC)) {
value &= ~GENMASK_ULL(31, 24);
value |= (u64)epp << 24;
}
+ WRITE_ONCE(cpudata->cppc_req_cached, value);
amd_pstate_set_epp(cpudata, epp);
skip_epp:
- WRITE_ONCE(cpudata->cppc_req_cached, value);
cpufreq_cpu_put(policy);
}
--
2.34.1
On Tue, Feb 14, 2023 at 03:58:11PM +0800, Karny, Wyes wrote:
> `amd_pstate_set_epp` function uses `cppc_req_cached` and `epp` variable
> to update the MSR_AMD_CPPC_REQ register for AMD MSR systems. The recent
> commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable
> use") changed the sequence of updating cppc_req_cached and writing the
> MSR_AMD_CPPC_REQ. Therefore while switching from powersave to
> performance governor and vice-versa in active mode MSR_AMD_CPPC_REQ is
> set with the previous cached value. To fix this: first update the
> `cppc_req_cached` variable and then call `amd_pstate_set_epp` function.
>
> - Before commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
> variable use"):
>
> With powersave governor:
> [ 1.652743] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
> [ 1.652744] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> [ 1.652746] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
>
> Changing to performance governor:
> [ 300.493842] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
> [ 300.493846] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> [ 300.493847] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
>
> - After commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
> variable use"):
>
> With powersave governor:
> [ 1.646037] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> [ 1.646038] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
> [ 1.646042] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
>
> Changing to performance governor:
> [ 687.117401] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> [ 687.117405] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
> [ 687.117419] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
>
> - After this fix:
>
> With powersave governor:
> [ 2.525717] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
> [ 2.525720] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> [ 2.525722] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
>
> Changing to performance governor:
> [ 3440.152468] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
> [ 3440.152473] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> [ 3440.152474] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
>
> Fixes: 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable use")
> Signed-off-by: Wyes Karny <[email protected]>
That's really nice catch! Thanks Wyes.
Acked-by: Huang Rui <[email protected]>
> ---
> drivers/cpufreq/amd-pstate.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index b8862afef4e4..45c88894fd8e 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1057,27 +1057,28 @@ static void amd_pstate_epp_init(unsigned int cpu)
>
> cpudata->epp_policy = cpudata->policy;
>
> - if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) {
> - epp = amd_pstate_get_epp(cpudata, value);
> - if (epp < 0)
> - goto skip_epp;
> - /* force the epp value to be zero for performance policy */
> - epp = 0;
> - } else {
> - /* Get BIOS pre-defined epp value */
> - epp = amd_pstate_get_epp(cpudata, value);
> - if (epp)
> - goto skip_epp;
> + /* Get BIOS pre-defined epp value */
> + epp = amd_pstate_get_epp(cpudata, value);
> + if (epp < 0) {
> + /**
> + * This return value can only be negative for shared_memory
> + * systems where EPP register read/write not supported.
> + */
> + goto skip_epp;
> }
> +
> + if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
> + epp = 0;
> +
> /* Set initial EPP value */
> if (boot_cpu_has(X86_FEATURE_CPPC)) {
> value &= ~GENMASK_ULL(31, 24);
> value |= (u64)epp << 24;
> }
>
> + WRITE_ONCE(cpudata->cppc_req_cached, value);
> amd_pstate_set_epp(cpudata, epp);
> skip_epp:
> - WRITE_ONCE(cpudata->cppc_req_cached, value);
> cpufreq_cpu_put(policy);
> }
>
> --
> 2.34.1
>
On Wed, Feb 15, 2023 at 1:35 PM Huang Rui <[email protected]> wrote:
>
> On Tue, Feb 14, 2023 at 03:58:11PM +0800, Karny, Wyes wrote:
> > `amd_pstate_set_epp` function uses `cppc_req_cached` and `epp` variable
> > to update the MSR_AMD_CPPC_REQ register for AMD MSR systems. The recent
> > commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable
> > use") changed the sequence of updating cppc_req_cached and writing the
> > MSR_AMD_CPPC_REQ. Therefore while switching from powersave to
> > performance governor and vice-versa in active mode MSR_AMD_CPPC_REQ is
> > set with the previous cached value. To fix this: first update the
> > `cppc_req_cached` variable and then call `amd_pstate_set_epp` function.
> >
> > - Before commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
> > variable use"):
> >
> > With powersave governor:
> > [ 1.652743] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
> > [ 1.652744] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> > [ 1.652746] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
> >
> > Changing to performance governor:
> > [ 300.493842] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
> > [ 300.493846] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> > [ 300.493847] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
> >
> > - After commit 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized
> > variable use"):
> >
> > With powersave governor:
> > [ 1.646037] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> > [ 1.646038] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
> > [ 1.646042] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
> >
> > Changing to performance governor:
> > [ 687.117401] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> > [ 687.117405] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
> > [ 687.117419] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
> >
> > - After this fix:
> >
> > With powersave governor:
> > [ 2.525717] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff
> > [ 2.525720] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff
> > [ 2.525722] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0
> >
> > Changing to performance governor:
> > [ 3440.152468] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff
> > [ 3440.152473] amd_pstate_set_epp: writing cppc_req_cached = 0xffff
> > [ 3440.152474] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0
> >
> > Fixes: 7cca9a9851a5 ("cpufreq: amd-pstate: avoid uninitialized variable use")
> > Signed-off-by: Wyes Karny <[email protected]>
>
> That's really nice catch! Thanks Wyes.
>
> Acked-by: Huang Rui <[email protected]>
Applied, thanks!