From: Sean Christopherson <seanjc@google.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
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>
Subject: Re: [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer
Date: Wed, 28 Apr 2021 22:56:50 +0000 [thread overview]
Message-ID: <YInoMjNJRgm3gUYX@google.com> (raw)
In-Reply-To: <1619608082-4187-1-git-send-email-wanpengli@tencent.com>
On Wed, Apr 28, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Commit ee66e453db13d (KVM: lapic: Busy wait for timer to expire when
> using hv_timer) tries to set ktime->expired_tscdeadline by checking
> ktime->hv_timer_in_use since lapic timer oneshot/periodic modes which
> are emulated by vmx preemption timer also get advanced, they leverage
> the same vmx preemption timer logic with tsc-deadline mode. However,
> ktime->hv_timer_in_use is cleared before apic_timer_expired() handling,
> let's delay this clearing in preemption-disabled region.
>
> Fixes: ee66e453db13d (KVM: lapic: Busy wait for timer to expire when using hv_timer)
Well that's embarassing. I suspect/hope I tested the case where start_hv_timer()
detects the timer already expired. On the plus side, start_hv_timer() calls
cancel_hv_timer() after apic_timer_expired(), so there are unlikely to be hidden
side effects (and cancel_hv_timer() is tiny).
> Cc: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/lapic.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 152591f..c0ebef5 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1913,8 +1913,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> if (!apic->lapic_timer.hv_timer_in_use)
> goto out;
> WARN_ON(rcuwait_active(&vcpu->wait));
> - cancel_hv_timer(apic);
> apic_timer_expired(apic, false);
> + cancel_hv_timer(apic);
>
> if (apic_lvtt_period(apic) && apic->lapic_timer.period) {
> advance_periodic_target_expiration(apic);
> --
> 2.7.4
>
next prev parent reply other threads:[~2021-04-28 22:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-28 11:08 [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer Wanpeng Li
2021-04-28 22:56 ` Sean Christopherson [this message]
2021-04-29 15:40 ` Paolo Bonzini
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=YInoMjNJRgm3gUYX@google.com \
--to=seanjc@google.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kernellwp@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).