linux-kernel - Re: [Patch v3 07/14] x86/hyperv: Change vTOM handling to use standard coco mechanisms

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Message-ID: <Y4XFjqEATqOgEnR6@zn.tnic>
Date:   Tue, 29 Nov 2022 09:40:46 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
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        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
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        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [Patch v3 07/14] x86/hyperv: Change vTOM handling to use
 standard coco mechanisms

On Tue, Nov 29, 2022 at 01:15:39AM +0000, Michael Kelley (LINUX) wrote:
> So that's why I'm suggesting CC_VENDOR_AMD_VTOM.

There's no CC_VENDOR_AMD_VTOM. How many times do I need to explain this?!
CC_VENDOR is well the CC vendor - not some special case.

IOW, the goal here is for generic SNP functionality to be the same for
*all* SNP guests. We won't do the AMD's version of vTOM enablement,
Hyper-V's version of vTOM enablement and so on. It must be a single
vTOM feature which works on *all* hypervisors as vTOM is a generic SNP
feature - not Hyper-V feature.

> Of course, when you go from N=1 hypervisors (i.e., KVM) to N=2 (KVM
> and Hyper-V, you find some places where incorrect assumptions were
> made or some generalizations are needed. Dexuan Cui's patch set for
> TDX support is fixing those places that he has encountered. But with
> those fixes, the TDX support will JustWork(tm) for Linux guests on
> Hyper-V.

That sounds like the right direction to take.

> I haven't gone deeply into the situation with AMD C-bit support on
> Hyper-V. Tianyu Lan's set of patches for that support is a bit bigger,
> and I'm planning to look closely to understand whether it's also just
> fixing incorrect assumptions and such, or whether they really are
> some differences with Hyper-V. If there are differences, I want to
> understand why.

You and me too. So I guess we should look at Tianyu's set first.

Thx.

-- 
Regards/Gruss,
    Boris.

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