Re: [PATCH v1 5/5] x86: Skip WBINVD instruction for VM guest

[Rafael J. Wysocki]

On Wed, Jun 9, 2021 at 11:51 PM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote:
>
> VM guests that supports ACPI, use standard ACPI mechanisms to signal
> sleep state entry (including reboot) to the host. The ACPI
> specification mandates WBINVD on any sleep state entry with the
> expectation that the platform is only responsible for maintaining the
> state of memory over sleep states, not preserving dirty data in any
> CPU caches. ACPI cache flushing requirements pre-date the advent of
> virtualization. Given guest sleep state entry does not affect any
> host power rails it is not required to flush caches. The host is
> responsible for maintaining cache state over its own bare metal sleep
> state transitions that power-off the cache. A TDX guest, unlike a
> typical guest, will machine check if the CPU cache is powered off.
>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Cc: linux-acpi@xxxxxxxxxxxxxxx
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
>  arch/x86/include/asm/acenv.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h
> index 9aff97f0de7f..d4162e94bee8 100644
> --- a/arch/x86/include/asm/acenv.h
> +++ b/arch/x86/include/asm/acenv.h
> @@ -10,10 +10,15 @@
>  #define _ASM_X86_ACENV_H
>
>  #include <asm/special_insns.h>
> +#include <asm/cpu.h>
>
>  /* Asm macros */
>
> -#define ACPI_FLUSH_CPU_CACHE() wbinvd()
> +#define ACPI_FLUSH_CPU_CACHE()                         \
> +do {                                                   \
> +       if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))      \
> +               wbinvd();                               \
> +} while (0)
>
>  int __acpi_acquire_global_lock(unsigned int *lock);
>  int __acpi_release_global_lock(unsigned int *lock);
> --
> 2.25.1
>