linux-kernel - Re: [PATCH v10 03/50] KVM: SEV: Do not intercept accesses to MSR_IA32

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Message-ID: <13d72960-c7bc-4bc2-8404-931d3de04ecf@redhat.com>
Date:   Wed, 13 Dec 2023 18:40:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, vkuznets@...hat.com, jmattson@...gle.com,
        luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
        pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
        pankaj.gupta@....com, liam.merwick@...cle.com,
        zhi.a.wang@...el.com, Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH v10 03/50] KVM: SEV: Do not intercept accesses to
 MSR_IA32_XSS for SEV-ES guests

On 12/13/23 18:30, Sean Christopherson wrote:
>> For now, all we can do is document our wishes, with which userspace had
>> better comply.  Please send a patch to QEMU that makes it obey.
> Discussed this early today with Paolo at PUCK and pointed out that (a) the CPU
> context switches the underlying state, (b) SVM doesn't allow intercepting*just*
> XSAVES, and (c) SNP's AP creation can bypass XSS interception.
> 
> So while we all (all == KVM folks) agree that this is rather terrifying, e.g.
> gives KVM zero option if there is a hardware issue, it's "fine" to let the guest
> use XSAVES/XSS.

Indeed; looks like I've got to queue this for 6.7 after all.

Paolo