linux-kernel - Re: [PATCH] KVM: X86: fix tlb_flush

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Message-ID: <YLedPIkBvPrjguCC@google.com>
Date:   Wed, 2 Jun 2021 15:01:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH] KVM: X86: fix tlb_flush_guest()

On Fri, May 28, 2021, Lai Jiangshan wrote:
> 
> On 2021/5/28 08:26, Sean Christopherson wrote:
> > On Fri, May 28, 2021, Lai Jiangshan wrote:
> > > 
> > > On 2021/5/28 00:13, Sean Christopherson wrote:
> > > > And making a request won't work without revamping the order of request handling
> > > > in vcpu_enter_guest(), e.g. KVM_REQ_MMU_RELOAD and KVM_REQ_MMU_SYNC are both
> > > > serviced before KVM_REQ_STEAL_UPDATE.
> > > 
> > > Yes, it just fixes the said problem in the simplest way.
> > > I copied KVM_REQ_MMU_RELOAD from kvm_handle_invpcid(INVPCID_TYPE_ALL_INCL_GLOBAL).
> > > (If the guest is not preempted, it will call invpcid_flush_all() and will be handled
> > > by this way)
> > 
> > The problem is that record_steal_time() is called after KVM_REQ_MMU_RELOAD
> > in vcpu_enter_guest() and so the reload request won't be recognized until the
> > next VM-Exit.  It works for kvm_handle_invpcid() because vcpu_enter_guest() is
> > guaranteed to run between the invcpid code and VM-Enter.
> 
> Kvm will recheck the request before VM-enter.
> See kvm_vcpu_exit_request().

Ah, right, forgot requests are rechecked.  Thanks!