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To:     Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org
Cc:     Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Cathy Avery <cavery@redhat.com>,
        Emanuele Giuseppe Esposito <eesposit@redhat.com>,
        linux-kernel@vger.kernel.org
References: <20210623074427.152266-1-vkuznets@redhat.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH RFC] KVM: nSVM: Fix L1 state corruption upon return from
 SMM
Message-ID: <a3918bfa-7b4f-c31a-448a-aa22a44d4dfd@redhat.com>
Date:   Wed, 23 Jun 2021 11:39:31 +0200
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On 23/06/21 09:44, Vitaly Kuznetsov wrote:
> - RFC: I'm not 100% sure my 'smart' idea to use currently-unused HSAVE area
> is that smart. Also, we don't even seem to check that L1 set it up upon
> nested VMRUN so hypervisors which don't do that may remain broken. A very
> much needed selftest is also missing.

It's certainly a bit weird, but I guess it counts as smart too.  It 
needs a few more comments, but I think it's a good solution.

One could delay the backwards memcpy until vmexit time, but that would 
require a new flag so it's not worth it for what is a pretty rare and 
already expensive case.

Paolo