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References: <20220302142806.51844-1-kirill.shutemov@linux.intel.com> <20220302142806.51844-30-kirill.shutemov@linux.intel.com>
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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 2 Mar 2022 08:13:05 -0800
Message-ID: <CAPcyv4gpCY5PW04T78M-0rkiGfXZGQTSdv31mV4LRXpxvWabeg@mail.gmail.com>
Subject: Re: [PATCHv5 29/30] ACPICA: Avoid cache flush inside virtual machines
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Juergen Gross <jgross@suse.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>, sdeep@vmware.com,
        Sean Christopherson <seanjc@google.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>, X86 ML <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Mar 2, 2022 at 6:28 AM Kirill A. Shutemov
<kirill.shutemov@linux.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@linux.intel.com>

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