Re: [PATCH] KVM: X86: fix tlb_flush_guest()

From: Sean Christopherson <seanjc@google.com>
To: Lai Jiangshan <laijs@linux.alibaba.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Lai Jiangshan" <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	kvm@vger.kernel.org, "Maxim Levitsky" <mlevitsk@redhat.com>
Subject: Re: [PATCH] KVM: X86: fix tlb_flush_guest()
Date: Wed, 2 Jun 2021 15:01:16 +0000	[thread overview]
Message-ID: <YLedPIkBvPrjguCC@google.com> (raw)
In-Reply-To: <332beac2-5a0b-2e5c-f22a-7609ed98acb9@linux.alibaba.com>

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!