kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Peter Xu <peterx@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Pei Zhang <pezhang@redhat.com>
Subject: Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device
Date: Tue, 11 May 2021 12:19:56 -0400	[thread overview]
Message-ID: <YJqurM+LiyAY+MPO@t490s> (raw)
In-Reply-To: <20210511145157.GC124427@fuller.cnet>

On Tue, May 11, 2021 at 11:51:57AM -0300, Marcelo Tosatti wrote:
> On Tue, May 11, 2021 at 10:39:11AM -0400, Peter Xu wrote:
> > On Fri, May 07, 2021 at 07:08:31PM -0300, Marcelo Tosatti wrote:
> > > > Wondering whether we should add a pi_test_on() check in kvm_vcpu_has_events()
> > > > somehow, so that even without customized ->vcpu_check_block we should be able
> > > > to break the block loop (as kvm_arch_vcpu_runnable will return true properly)?
> > > 
> > > static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> > > {
> > >         int ret = -EINTR;
> > >         int idx = srcu_read_lock(&vcpu->kvm->srcu);
> > > 
> > >         if (kvm_arch_vcpu_runnable(vcpu)) {
> > >                 kvm_make_request(KVM_REQ_UNHALT, vcpu); <---
> > >                 goto out;
> > >         }
> > > 
> > > Don't want to unhalt the vcpu.
> > 
> > Could you elaborate?  It's not obvious to me why we can't do that if
> > pi_test_on() returns true..  we have pending post interrupts anyways, so
> > shouldn't we stop halting?  Thanks!
> 
> pi_test_on() only returns true when an interrupt is signalled by the
> device. But the sequence of events is:
> 
> 
> 1. pCPU idles without notification vector configured to wakeup vector.
> 
> 2. PCI device is hotplugged, assigned device count increases from 0 to 1.
> 
> <arbitrary amount of time>
> 
> 3. device generates interrupt, sets ON bit to true in the posted
> interrupt descriptor.
> 
> We want to exit kvm_vcpu_block after 2, but before 3 (where ON bit
> is not set).

Ah yes.. thanks.

Besides the current approach, I'm thinking maybe it'll be cleaner/less LOC to
define a KVM_REQ_UNBLOCK to replace the pre_block hook (in x86's kvm_host.h):

#define KVM_REQ_UNBLOCK			KVM_ARCH_REQ(31)

We can set it in vmx_pi_start_assignment(), then check+clear it in
kvm_vcpu_has_events() (or make it a bool in kvm_vcpu struct?).

The thing is current vmx_vcpu_check_block() is mostly a sanity check and
copy-paste of the pi checks on a few items, so maybe cleaner to use
KVM_REQ_UNBLOCK, as it might be reused in the future for re-evaluating of
pre-block for similar purpose?

No strong opinion, though.

-- 
Peter Xu


  reply	other threads:[~2021-05-11 16:20 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07 13:06 [patch 0/4] VMX: configure posted interrupt " Marcelo Tosatti
2021-05-07 13:06 ` [patch 1/4] KVM: x86: add start_assignment hook to kvm_x86_ops Marcelo Tosatti
2021-05-07 19:16   ` Peter Xu
2021-05-10 17:53     ` Marcelo Tosatti
2021-05-07 13:06 ` [patch 2/4] KVM: add arch specific vcpu_check_block callback Marcelo Tosatti
2021-05-07 13:06 ` [patch 3/4] KVM: x86: implement kvm_arch_vcpu_check_block callback Marcelo Tosatti
2021-05-07 13:06 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-07 17:22   ` Sean Christopherson
2021-05-07 19:29     ` Peter Xu
2021-05-07 22:08       ` Marcelo Tosatti
2021-05-11 14:39         ` Peter Xu
2021-05-11 14:51           ` Marcelo Tosatti
2021-05-11 16:19             ` Peter Xu [this message]
2021-05-11 17:18               ` Marcelo Tosatti
2021-05-11 21:35                 ` Peter Xu
2021-05-11 23:51                   ` Marcelo Tosatti
2021-05-12  0:02                     ` Marcelo Tosatti
2021-05-12  0:38                       ` Peter Xu
2021-05-12 11:10                         ` Marcelo Tosatti
2021-05-12 14:41                       ` Sean Christopherson
2021-05-12 15:34                         ` Peter Xu
2021-05-10 17:26 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v3) Marcelo Tosatti
2021-05-10 17:26 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-24 15:55   ` Paolo Bonzini
2021-05-24 17:53     ` Marcelo Tosatti
2021-05-25 11:58       ` Paolo Bonzini
2021-05-11 23:57 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v4) Marcelo Tosatti
2021-05-11 23:57 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YJqurM+LiyAY+MPO@t490s \
    --to=peterx@redhat.com \
    --cc=alex.williamson@redhat.com \
    --cc=kvm@vger.kernel.org \
    --cc=mtosatti@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=pezhang@redhat.com \
    --cc=seanjc@google.com \
    --subject='Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).