linux-kernel - Re: [PATCH 03/13] KVM: x86: Set KVM_REQ_EVENT if run is canceled with req_immediate

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Message-ID: <CALMp9eR9bVK4p2ca-N+=PThmMF2UhzE8DvBDUke69ygDE34Uaw@mail.gmail.com>
Date:   Tue, 28 Apr 2020 14:41:11 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH 03/13] KVM: x86: Set KVM_REQ_EVENT if run is canceled with
 req_immediate_exit set

On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Re-request KVM_REQ_EVENT if vcpu_enter_guest() bails after processing
> pending requests and an immediate exit was requested.  This fixes a bug
> where a pending event, e.g. VMX preemption timer, is delayed and/or lost
> if the exit was deferred due to something other than a higher priority
> _injected_ event, e.g. due to a pending nested VM-Enter.  This bug only
> affects the !injected case as kvm_x86_ops.cancel_injection() sets
> KVM_REQ_EVENT to redo the injection, but that's purely serendipitous
> behavior with respect to the deferred event.
>
> Note, emulated preemption timer isn't the only event that can be
> affected, it simply happens to be the only event where not re-requesting
> KVM_REQ_EVENT is blatantly visible to the guest.
>
> Fixes: f4124500c2c13 ("KVM: nVMX: Fully emulate preemption timer")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>