linux-kernel - Re: [PATCHv13 9/9] x86/tdx: Add unaccepted memory support

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Date:   Mon, 5 Jun 2023 12:18:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        aarcange@...hat.com, peterx@...hat.com, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv13 9/9] x86/tdx: Add unaccepted memory support

On 6/2/23 07:26, Tom Lendacky wrote:
>> So this is a change in this version. If tdx_accept_memory() fails,
>> you'll report unknown platform. Wouldn't it be better to have an error
>> message that indicates a failure in the accept path?
>>
> 
> Maybe you can keep it similar to the v12 version with just a new error
> message, something like:
> 
>     if (early_is_tdx_guest()) {
>         if (!tdx_accept_memory(start, end))
>             error("TDX error accepting memory\n");
>     } else {
>         error("Cannot accept memory: unknown platform\n");
>     }

In the end, these errors aren't plumbed out to the page allocator.  They
*need* to succeed or we are dead anyway.  Should we just send a fatal
error up to the TDX module when we fail to accept memory?  It's
_slightly_ less opaque than plowing into an unaccepted page.