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Date:   Tue, 16 May 2023 13:03:32 -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>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        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>,
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        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>
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From:   Dave Hansen <dave.hansen@intel.com>
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On 5/16/23 11:35, Ard Biesheuvel wrote:
>>> 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).
>>
> OK, and so the architecture stipulates that prefetching or other
> speculative accesses must never deliver exceptions to the host
> regarding such ranges?

I don't know of anywhere that this is explicitly written.  It's probably
implicit _somewhere_ in the reams of VMX/TDX and base SDM docs, but heck
if I know where it is. :)

If this is something anyone wants to see added to the SEPT_VE_DISABLE
documentation, please speak up.  I don't think it would be hard to get
it added and provide an explicit guarantee.