linux-kernel - Re: [PATCH 2/9] KVM: x86: Emulate triple fault shutdown if RSM emulation fails

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Date:   Thu, 10 Jun 2021 15:23:27 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     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+fb0b6a7e8713aeb0319c@...kaller.appspotmail.com
Subject: Re: [PATCH 2/9] KVM: x86: Emulate triple fault shutdown if RSM
 emulation fails

On 09/06/21 20:56, Sean Christopherson wrote:
> For recent Intel CPUs, restoring NMI blocking is technically wrong, but
> so is restoring NMI blocking in the first place, and Intel's RSM
> "architecture" is such a mess that just about anything is allowed and can
> be justified as micro-architectural behavior.

The Intel manual is an absolute mess with respect to NMI blocking, and 
for once AMD followed suit.

Some versions of the AMD BIOS and Kernel Developer Manual provide the 
offset of the "NMI masked" flag in the SMM state save area, but 
unfortunately that was discovered too late.

Paolo