linux-kernel - Re: [PATCH v2 1/2] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

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Message-ID: <CANRm+CzFdJvuq=V+5eSGmqvrTFPyHTHGp-rQD4gGujADeNtf+w@mail.gmail.com>
Date:   Thu, 12 May 2022 16:23:40 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 1/2] KVM: LAPIC: Disarm LAPIC timer includes pending
 timer around TSC deadline switch

On Wed, 11 May 2022 at 21:54, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 5/11/22 04:38, Wanpeng Li wrote:
> >
> > Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> > Signed-off-by: Wanpeng Li<wanpengli@...cent.com>
> > ---
>
> Please write a testcase for this.

Something like this, however, it is not easy to catch the pending
timer in this scenario.

diff --git a/x86/apic.c b/x86/apic.c
index 23508ad..108c1c8 100644
--- a/x86/apic.c
+++ b/x86/apic.c
@@ -22,7 +22,7 @@ static void test_lapic_existence(void)
 #define TSC_DEADLINE_TIMER_VECTOR 0xef
 #define BROADCAST_VECTOR 0xcf

-static int tdt_count;
+static int volatile tdt_count;

 static void tsc_deadline_timer_isr(isr_regs_t *regs)
 {
@@ -672,6 +672,18 @@ static void test_apic_change_mode(void)
        /* now tmcct == 0 and tmict != 0 */
        apic_change_mode(APIC_LVT_TIMER_PERIODIC);
        report(!apic_read(APIC_TMCCT), "TMCCT should stay at zero");
+
+       handle_irq(TSC_DEADLINE_TIMER_VECTOR, tsc_deadline_timer_isr);
+       irq_enable();
+
+       apic_write(APIC_LVTT, APIC_LVT_TIMER_ONESHOT |
+               APIC_LVT_TIMER_VECTOR);
+        /* Divider == 1 */
+       apic_write(APIC_TDCR, 0x0000000b);
+
+       apic_write(APIC_TMICT, 0x999999);
+       enable_tsc_deadline_timer();
+       while(tdt_count == 1);
 }

 #define KVM_HC_SEND_IPI 10