Subject: Re: [PATCH v8 20/40] x86/sev: Use SEV-SNP AP creation to start
 secondary CPUs
To:     Brijesh Singh <brijesh.singh@amd.com>,
        Borislav Petkov <bp@alien8.de>,
        Vlastimil Babka <vbabka@suse.cz>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Michael Roth <michael.roth@amd.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-21-brijesh.singh@amd.com> <Yc8jerEP5CrxfFi4@zn.tnic>
 <75c0605f-7ed0-abcc-4855-dae5d87d0861@amd.com>
From:   Tom Lendacky <thomas.lendacky@amd.com>
Message-ID: <346da2f7-220f-83bd-2dbf-29e681fc089b@amd.com>
Date:   Wed, 12 Jan 2022 11:10:04 -0600
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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?
>