linux-kernel - Re: [PATCH v10 1/2] x86/tdx: Retry partially-completed page conversion hypercalls

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Message-ID: <66a888f8-45ec-ee9f-0a33-71460e41e540@intel.com>
Date:   Thu, 7 Sep 2023 14:13:12 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dexuan Cui <decui@...rosoft.com>, x86@...nel.org,
        ak@...ux.intel.com, arnd@...db.de, bp@...en8.de,
        brijesh.singh@....com, dan.j.williams@...el.com,
        dave.hansen@...ux.intel.com, haiyangz@...rosoft.com, hpa@...or.com,
        jane.chu@...cle.com, kirill.shutemov@...ux.intel.com,
        kys@...rosoft.com, luto@...nel.org, mingo@...hat.com,
        peterz@...radead.org, rostedt@...dmis.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
        tglx@...utronix.de, tony.luck@...el.com, wei.liu@...nel.org,
        Jason@...c4.com, nik.borisov@...e.com, mikelley@...rosoft.com
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tianyu.Lan@...rosoft.com, rick.p.edgecombe@...el.com,
        andavis@...hat.com, mheslin@...hat.com, vkuznets@...hat.com,
        xiaoyao.li@...el.com
Subject: Re: [PATCH v10 1/2] x86/tdx: Retry partially-completed page
 conversion hypercalls

On 8/11/23 14:48, Dexuan Cui wrote:
> TDX guest memory is private by default and the VMM may not access it.
> However, in cases where the guest needs to share data with the VMM,
> the guest and the VMM can coordinate to make memory shared between
> them.
> 
> The guest side of this protocol includes the "MapGPA" hypercall.  This
> call takes a guest physical address range.  The hypercall spec (aka.
> the GHCI) says that the MapGPA call is allowed to return partial
> progress in mapping this range and indicate that fact with a special
> error code.  A guest that sees such partial progress is expected to
> retry the operation for the portion of the address range that was not
> completed.
> 
> Hyper-V does this partial completion dance when set_memory_decrypted()
> is called to "decrypt" swiotlb bounce buffers that can be up to 1GB
> in size.  It is evidently the only VMM that does this, which is why
> nobody noticed this until now.
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>

Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>

Is there any reason that this needs to go into the stable trees?  If so,
Fixes: and Cc:stable@ tags would be nice.