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

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Date:   Thu, 10 Jun 2021 15:00:10 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v1 5/5] x86: Skip WBINVD instruction for VM guest

On Wed, Jun 9, 2021 at 11:51 PM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> 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@...ysocki.net>
> Cc: linux-acpi@...r.kernel.org
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

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

> ---
>  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
>