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Date:   Tue, 16 May 2023 11:27:16 -0700
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Subject: Re: [PATCHv11 6/9] efi/unaccepted: Avoid load_unaligned_zeropad()
 stepping into unaccepted memory
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To:     Ard Biesheuvel <ardb@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        marcelo.cerri@canonical.com, tim.gardner@canonical.com,
        khalid.elmously@canonical.com, philip.cox@canonical.com,
        aarcange@redhat.com, peterx@redhat.com, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>
References: <20230513220418.19357-1-kirill.shutemov@linux.intel.com>
 <20230513220418.19357-7-kirill.shutemov@linux.intel.com>
 <CAMj1kXG488uW=dpvbfvdN1fMZVJ3kCZQoW3UVQJW1F2VEXyxHg@mail.gmail.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <CAMj1kXG488uW=dpvbfvdN1fMZVJ3kCZQoW3UVQJW1F2VEXyxHg@mail.gmail.com>
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On 5/16/23 11:08, Ard Biesheuvel wrote:
>> But, this approach does not work for unaccepted memory. For TDX, a load
>> from unaccepted memory will not lead to a recoverable exception within
>> the guest. The guest will exit to the VMM where the only recourse is to
>> terminate the guest.
>>
> Does this mean that the kernel maps memory before accepting it? As
> otherwise, I would assume that such an access would page fault inside
> the guest before triggering an exception related to the unaccepted
> state.

Yes, the kernel maps memory before accepting it (modulo things like
DEBUG_PAGEALLOC).