linux-kernel - Re: [PATCH v2 05/21] KVM: nVMX: Prioritize TSS T-flag #DBs over Monitor Trap Flag

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Message-ID: <CALMp9eSH1O8keAVxZzfdvV1vu0AJBhaXVUfkSgYgCPOoSB5=Jw@mail.gmail.com>
Date:   Wed, 6 Jul 2022 16:51:50 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH v2 05/21] KVM: nVMX: Prioritize TSS T-flag #DBs over
 Monitor Trap Flag

On Tue, Jun 14, 2022 at 1:47 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Service TSS T-flag #DBs prior to pending MTFs, as such #DBs are higher
> priority than MTF.  KVM itself doesn't emulate TSS #DBs, and any such

Is there a KVM erratum for that?

> exceptions injected from L1 will be handled by hardware (or morphed to
> a fault-like exception if injection fails), but theoretically userspace
> could pend a TSS T-flag #DB in conjunction with a pending MTF.
>
> Note, there's no known use case this fixes, it's purely to be technically
> correct with respect to Intel's SDM.

A test would be nice. :-)