linux-kernel - Re: [PATCH] KVM: x86: Forcibly leave nested virt when SMM state is toggled

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Date:   Wed, 26 Jan 2022 16:08:04 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+8112db3ab20e70d50c31@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: x86: Forcibly leave nested virt when SMM state is
 toggled

On Wed, Jan 26, 2022, Maxim Levitsky wrote:
> On Tue, 2022-01-25 at 22:03 +0000, Sean Christopherson wrote:
> > Peeking at QEMU source, AFAICT QEMU restores nested state before events,
> > but I don't see how that can possibly work.  I assume QEMU does something
> > where it restores the "run" state first and then does a full restore?
> 
> Well, according to my testing, nested migration with SMM *is* still quite broken,
> (on both SVM and VMX)
> resulting in various issues up to L1 crash. 
> 
> When I last tackled SMM, I fixed most issues that
> happen just when the L2 is running and I inject flood of SMIs to L1 - even that
> was crashing things all around, so this might be as well the reason for that.

Heh, that would certainly explain why QEMU's code looks broken.  Thanks!