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

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Message-ID: <SA1PR21MB13352E893E8DCAE02CED2857BF1FA@SA1PR21MB1335.namprd21.prod.outlook.com>
Date:   Tue, 22 Aug 2023 16:47:09 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Isaku Yamahata <isaku.yamahata@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "bp@...en8.de" <bp@...en8.de>, "arnd@...db.de" <arnd@...db.de>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>
CC:     "brijesh.singh@....com" <brijesh.singh@....com>,
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        Haiyang Zhang <haiyangz@...rosoft.com>,
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        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
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Subject: RE: [PATCH v10 1/2] x86/tdx: Retry partially-completed page
 conversion hypercalls

> From: Isaku Yamahata <isaku.yamahata@...il.com>
> Sent: Monday, August 14, 2023 12:04 PM
> To: Dexuan Cui <decui@...rosoft.com>
> [...]
> 
> On Fri, Aug 11, 2023 at 02:48:25PM -0700,
> Dexuan Cui <decui@...rosoft.com> 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.
> 
> Now TDX KVM + TDX qemu supports partial completion because TD guest
> can pass
> very large range. e.g. 1GB order.  I tested this patch with (patched) TDX
> KVM/qemu.
> 
> Reviewed-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Tested-by: Isaku Yamahata <isaku.yamahata@...el.com>

Thanks Isaku for reviewing and testing the patch!

@Dave, may I know if the 2 updated patches look good to you?