Re: [PATCH v2] acpi/processor: sanitize _PDC buffer bits when running as Xen dom0

["Wilczynski, Michal" <michal.wilczynski@xxxxxxxxx>]

Hi,

On 9/6/2023 8:21 PM, Jason Andryuk wrote:
> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
>
> The Processor _PDC buffer bits notify ACPI of the OS capabilities, and
> so ACPI can adjust the return of other Processor methods taking the OS
> capabilities into account.

_PDC method is deprecated for this purpose, since 2018, and is dropped from
spec since 6.5

We made the switch in linux since 6.6:
95272641338a ("ACPI: processor: Use _OSC to convey OSPM processor support 
information")

>
> When Linux is running as a Xen dom0, it's the hypervisor the entity
> in charge of processor power management, and hence Xen needs to make
> sure the capabilities reported in the _PDC buffer match the
> capabilities of the driver in Xen.

So I guess you would need to sanitize buffer passed to _OSC method instead ?

>
> Introduce a small helper to sanitize the buffer when running as Xen
> dom0.
>
> When Xen supports HWP, this serves as the equivalent of commit
> a21211672c9a ("ACPI / processor: Request native thermal interrupt
> handling via _OSC") to avoid SMM crashes.  Xen will set bit 12 in the
> _PDC bits and the _PDC call will apply it.
>
> [ jandryuk: Mention Xen HWP's need.  Move local variables ]
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---
> v2:
> Move local variables in acpi_processor_eval_pdc() to reuse in both conditions.
> ---
>  arch/x86/include/asm/xen/hypervisor.h |  6 ++++++
>  arch/x86/xen/enlighten.c              | 19 +++++++++++++++++++
>  drivers/acpi/processor_pdc.c          | 22 ++++++++++++++++------
>  3 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/hypervisor.h 
> b/arch/x86/include/asm/xen/hypervisor.h
> index 5fc35f889cd1..0f88a7e450d3 100644
> --- a/arch/x86/include/asm/xen/hypervisor.h
> +++ b/arch/x86/include/asm/xen/hypervisor.h
> @@ -63,4 +63,10 @@ void __init xen_pvh_init(struct boot_params *boot_params);
>  void __init mem_map_via_hcall(struct boot_params *boot_params_p);
>  #endif
>  
> +#ifdef CONFIG_XEN_DOM0
> +void xen_sanitize_pdc(uint32_t *buf);
> +#else
> +static inline void xen_sanitize_pdc(uint32_t *buf) { BUG(); }
> +#endif
> +
>  #endif /* _ASM_X86_XEN_HYPERVISOR_H */
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index b8db2148c07d..9f7fc11330a3 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -346,3 +346,22 @@ void xen_arch_unregister_cpu(int num)
>  }
>  EXPORT_SYMBOL(xen_arch_unregister_cpu);
>  #endif
> +
> +#ifdef CONFIG_XEN_DOM0
> +void xen_sanitize_pdc(uint32_t *buf)
> +{
> +     struct xen_platform_op op = {
> +             .cmd                    = XENPF_set_processor_pminfo,
> +             .interface_version      = XENPF_INTERFACE_VERSION,
> +             .u.set_pminfo.id        = -1,
> +             .u.set_pminfo.type      = XEN_PM_PDC,
> +     };
> +     int ret;
> +
> +     set_xen_guest_handle(op.u.set_pminfo.pdc, buf);
> +     ret = HYPERVISOR_platform_op(&op);
> +     if (ret)
> +             pr_info("sanitize of _PDC buffer bits from Xen failed: %d\n",
> +                     ret);
> +}
> +#endif
> diff --git a/drivers/acpi/processor_pdc.c b/drivers/acpi/processor_pdc.c
> index 18fb04523f93..9393dd4a3158 100644
> --- a/drivers/acpi/processor_pdc.c
> +++ b/drivers/acpi/processor_pdc.c
> @@ -122,6 +122,11 @@ static acpi_status
>  acpi_processor_eval_pdc(acpi_handle handle, struct acpi_object_list *pdc_in)
>  {
>       acpi_status status = AE_OK;
> +     union acpi_object *obj;
> +     u32 *buffer = NULL;
> +
> +     obj = pdc_in->pointer;
> +     buffer = (u32 *)(obj->buffer.pointer);
>  
>       if (boot_option_idle_override == IDLE_NOMWAIT) {
>               /*
> @@ -129,14 +134,19 @@ acpi_processor_eval_pdc(acpi_handle handle, struct 
> acpi_object_list *pdc_in)
>                * mode will be disabled in the parameter of _PDC object.
>                * Of course C1_FFH access mode will also be disabled.
>                */
> -             union acpi_object *obj;
> -             u32 *buffer = NULL;
> -
> -             obj = pdc_in->pointer;
> -             buffer = (u32 *)(obj->buffer.pointer);
>               buffer[2] &= ~(ACPI_PDC_C_C2C3_FFH | ACPI_PDC_C_C1_FFH);
> -
>       }
> +
> +     if (xen_initial_domain()) {
> +             /*
> +              * When Linux is running as Xen dom0, the hypervisor is the
> +              * entity in charge of the processor power management, and so
> +              * Xen needs to check the OS capabilities reported in the _PDC
> +              * buffer matches what the hypervisor driver supports.
> +              */
> +             xen_sanitize_pdc(buffer);
> +     }
> +
>       status = acpi_evaluate_object(handle, "_PDC", pdc_in, NULL);
>  
>       if (ACPI_FAILURE(status))