linux-kernel - Re: [PATCH v8 20/40] x86/sev: Use SEV-SNP AP creation to start secondary CPUs

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Message-ID: <346da2f7-220f-83bd-2dbf-29e681fc089b@amd.com>
Date:   Wed, 12 Jan 2022 11:10:04 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Brijesh Singh <brijesh.singh@....com>,
        Borislav Petkov <bp@...en8.de>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 20/40] x86/sev: Use SEV-SNP AP creation to start
 secondary CPUs

On 1/12/22 10:33 AM, Brijesh Singh wrote:
> On 12/31/21 9:36 AM, Borislav Petkov wrote:
>> On Fri, Dec 10, 2021 at 09:43:12AM -0600, Brijesh Singh wrote:

>>> +     * an attempt was done to use the current VMSA with a running vCPU, a
>>> +     * #VMEXIT of that vCPU would wipe out all of the settings being done
>>> +     * here.
>>
>> I don't understand - this is waking up a CPU, how can it ever be a
>> running vCPU which is using the current VMSA?!

Yes, in general. My thought was that nothing is stopping a malicious 
hypervisor from performing a VMRUN on that vCPU and then the VMSA would be 
in use.

Thanks,
Tom

>>
>> There is per_cpu(snp_vmsa, cpu), who else can be using that one currently?
>>
> 
> Maybe Tom can expand it bit more?
>