Re: [PATCH] ACPI: CPPC: Fix uninitialized ref variable in cppc_get_perf_caps

[Rafael J. Wysocki]

On Wed, Mar 11, 2026 at 8:13 AM Pengjie Zhang <zhangpengjie2@xxxxxxxxxx> wrote:
>
> Commit 8505bfb4e4ec ("ACPI: CPPC: Move reference performance
> to capabilities") introduced a logical error when retrieving
> the reference performance.
>
> On platforms lacking the reference performance register, the fallback
> logic leaves the local 'ref' variable uninitialized (0). This causes
> the subsequent sanity check to incorrectly return -EFAULT, breaking
> amd_pstate initialization.
>
> Fix this by assigning 'ref = nom' in the fallback path.
>
> Fixes: 8505bfb4e4ec ("ACPI: CPPC: Move reference performance to capabilities")
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20260310003026.GA2639793@ax162/
> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Signed-off-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
> ---
> This is on top of linux-next.
> ---
>  drivers/acpi/cppc_acpi.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 07bbf5b366a4..5ad922eb937a 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1407,12 +1407,11 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
>          * If reference perf register is not supported then we should
>          * use the nominal perf value
>          */
> -       if (CPC_SUPPORTED(reference_reg)) {
> +       if (CPC_SUPPORTED(reference_reg))
>                 cpc_read(cpunum, reference_reg, &ref);
> -               perf_caps->reference_perf = ref;
> -       } else {
> -               perf_caps->reference_perf = nom;
> -       }
> +       else
> +               ref = nom;
> +       perf_caps->reference_perf = ref;
>
>         if (guaranteed_reg->type != ACPI_TYPE_BUFFER  ||
>             IS_NULL_REG(&guaranteed_reg->cpc_entry.reg)) {
> --

Applied, thanks!