linux-kernel - Re: [PATCHv5 29/30] ACPICA: Avoid cache flush inside virtual machines

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Message-ID: <CAPcyv4gpCY5PW04T78M-0rkiGfXZGQTSdv31mV4LRXpxvWabeg@mail.gmail.com>
Date:   Wed, 2 Mar 2022 08:13:05 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Juergen Gross <jgross@...e.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, sdeep@...are.com,
        Sean Christopherson <seanjc@...gle.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>, X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 29/30] ACPICA: Avoid cache flush inside virtual machines

On Wed, Mar 2, 2022 at 6:28 AM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> WBINVD is not supported in TDX guest and triggers #VE. There's no robust
> way to emulate it. The kernel has to avoid it.
>
> ACPI_FLUSH_CPU_CACHE() flushes caches usign WBINVD on entering sleep
> states. It is required to prevent data loss.
>
> While running inside virtual machine, the kernel can bypass cache
> flushing. Changing sleep state in a virtual machine doesn't affect the
> host system sleep state and cannot lead to data loss.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Reviewed-by: Dan Williams <dan.j.williams@...el.com>