From: Wanpeng Li <kernellwp@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Jim Mattson <jmattson@google.com>,
LKML <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 2/2] KVM: LAPIC: reset TMCCT during vCPU reset
Date: Tue, 8 Jun 2021 08:31:02 +0800 [thread overview]
Message-ID: <CANRm+CxQc+fiO5jBDif9M5jUKRCU-mHtb5yMaPsbRpWR+v2hYQ@mail.gmail.com> (raw)
In-Reply-To: <YLj2jDKMYZatdl3a@google.com>
On Thu, 3 Jun 2021 at 23:34, Sean Christopherson <seanjc@google.com> wrote:
>
> On Thu, Jun 03, 2021, Jim Mattson wrote:
> > On Thu, Jun 3, 2021 at 2:01 AM Wanpeng Li <kernellwp@gmail.com> wrote:
> > >
> > > From: Wanpeng Li <wanpengli@tencent.com>
> > >
> > > The value of current counter register after reset is 0 for both Intel
> > > and AMD, let's do it in kvm.
> > >
> > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> >
> > How did we miss that?
>
> I suspect it's not actually a functional issue, and that writing '0' at reset is
> a glorified nop. The TMCCT is always computed on-demand and never directly
> readable.
Update the patch description in v2, thanks.
Wanpeng
>
> Is there an observable bug being fixed? If not, the changelog should state that
> this is a cosmetic change of sorts.
>
> static u32 __apic_read(struct kvm_lapic *apic, unsigned int offset)
> {
> u32 val = 0;
>
> if (offset >= LAPIC_MMIO_LENGTH)
> return 0;
>
> switch (offset) {
> case APIC_ARBPRI:
> break;
>
> case APIC_TMCCT: /* Timer CCR */
> if (apic_lvtt_tscdeadline(apic))
> return 0;
>
> val = apic_get_tmcct(apic);
> break;
> ...
> }
>
>
> static u32 apic_get_tmcct(struct kvm_lapic *apic)
> {
> ktime_t remaining, now;
> s64 ns;
> u32 tmcct;
>
> ASSERT(apic != NULL);
>
> /* if initial count is 0, current count should also be 0 */
> if (kvm_lapic_get_reg(apic, APIC_TMICT) == 0 || <------------
> apic->lapic_timer.period == 0)
> return 0;
>
> now = ktime_get();
> remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
> if (ktime_to_ns(remaining) < 0)
> remaining = 0;
>
> ns = mod_64(ktime_to_ns(remaining), apic->lapic_timer.period);
> tmcct = div64_u64(ns,
> (APIC_BUS_CYCLE_NS * apic->divide_count));
>
> return tmcct;
> }
>
> int kvm_apic_get_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
> {
> memcpy(s->regs, vcpu->arch.apic->regs, sizeof(*s));
>
> /*
> * Get calculated timer current count for remaining timer period (if
> * any) and store it in the returned register set.
> */
> __kvm_lapic_set_reg(s->regs, APIC_TMCCT,
> __apic_read(vcpu->arch.apic, APIC_TMCCT)); <----
>
> return kvm_apic_state_fixup(vcpu, s, false);
> }
>
>
>
next prev parent reply other threads:[~2021-06-08 0:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 9:00 [PATCH 1/2] KVM: LAPIC: write 0 to TMICT should also cancel vmx-preemption timer Wanpeng Li
2021-06-03 9:00 ` [PATCH 2/2] KVM: LAPIC: reset TMCCT during vCPU reset Wanpeng Li
2021-06-03 12:27 ` Jim Mattson
2021-06-03 15:34 ` Sean Christopherson
2021-06-08 0:31 ` Wanpeng Li [this message]
2021-06-03 15:20 ` [PATCH 1/2] KVM: LAPIC: write 0 to TMICT should also cancel vmx-preemption timer Sean Christopherson
2021-06-04 0:36 ` Wanpeng Li
2021-06-04 15:37 ` Sean Christopherson
2021-06-08 0:30 ` Wanpeng Li
2021-06-03 23:02 ` David Matlack
2021-06-04 0:32 ` Wanpeng Li
2021-06-04 15:59 ` David Matlack
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=CANRm+CxQc+fiO5jBDif9M5jUKRCU-mHtb5yMaPsbRpWR+v2hYQ@mail.gmail.com \
--to=kernellwp@gmail.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.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).