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Date:   Mon, 28 Nov 2022 20:56:31 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>
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Subject: Re: [Patch v3 07/14] x86/hyperv: Change vTOM handling to use
 standard coco mechanisms
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References: <1668624097-14884-8-git-send-email-mikelley@microsoft.com>
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On Mon, Nov 28, 2022 at 05:55:11PM +0000, Michael Kelley (LINUX) wrote:
> But vendor AMD effectively offers two different encryption schemes that
> could be seen by the guest VM.  The hypervisor chooses which scheme a
> particular guest will see.  Hyper-V has chosen to present the vTOM scheme
> to guest VMs, including normal Linux and Windows guests, that have been
> modestly updated to understand vTOM.

If this is a standard SNP guest then you can detect vTOM support using
SEV_FEATURES. See this thread here:

https://lore.kernel.org/r/20221117044433.244656-1-nikunj@amd.com

Which then means, you don't need any special gunk except extending this
patch above to check SNP has vTOM support.

> In the future, Hyper-V may also choose to present original AMD C-bit scheme
> in some guest VMs, depending on the use case.  And it will present the Intel
> TDX scheme when running on that hardware.

And all those should JustWork(tm) because we already support such guests.

> To my knowledge, KVM does not support the AMD vTOM scheme.
> Someone from AMD may have a better sense whether adding that
> support is likely in the future.

Yah, see above.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette