Re: [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts

From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Mingwei Zhang <mizhang@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Oliver Upton <oupton@google.com>
Subject: Re: [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts
Date: Thu, 25 Aug 2022 00:11:44 +0000	[thread overview]
Message-ID: <Ywa+QL/kDp9ibkbC@google.com> (raw)
In-Reply-To: <17505e309d02cf5a96e33f75ccdd6437a8c79222.camel@redhat.com>

On Wed, Aug 03, 2022, Maxim Levitsky wrote:
> On Wed, 2022-08-03 at 10:51 -0700, Mingwei Zhang wrote:
> > On Wed, Aug 3, 2022 at 10:18 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
> > > On 8/3/22 01:07, Mingwei Zhang wrote:
> > > > +     /*
> > > > +      * We must first get the vmcs12 pages before checking for interrupts
> > > > +      * that might unblock the guest if L1 is using virtual-interrupt
> > > > +      * delivery.
> > > > +      */
> > > > +     if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
> > > > +             /*
> > > > +              * If we have to ask user-space to post-copy a page,
> > > > +              * then we have to keep trying to get all of the
> > > > +              * VMCS12 pages until we succeed.
> > > > +              */
> > > > +             if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
> > > > +                     kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
> > > > +                     return 0;
> > > > +             }
> > > > +     }
> > > > +
> > > 
> > > I think request handling (except for KVM_REQ_EVENT) could be more
> > > generically moved from vcpu_enter_guest() to vcpu_run().
> > 
> > Yeah, sounds good to me. I can come up with an updated version. At
> > least, I will remove the repeat request here.
> 
> Now it all makes sense. I do think that KVM_REQ_GET_NESTED_STATE_PAGES processing
> when the vCPU is halted is indeed missing.
> 
> This reminds me that I would be *very* happy to remove the KVM_REQ_GET_NESTED_STATE_PAGES,
> if by any chance there is an agreement to do so upstream.
> This is yet another reason to do so to be honest.
> Just my 0.2 cents of course.

+100

@google folks, what would it take for us to mark KVM_REQ_GET_NESTED_STATE_PAGES
as deprecated in upstream and stop accepting patches/fixes?  IIUC, when we eventually
move to userfaultfd, all this goes away, i.e. we do want to ditch this at some point.