linux-kernel - [PATCH 5.15 034/171] KVM: LAPIC: Also cancel preemption timer during SET

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Message-Id: <20220131105231.168825677@linuxfoundation.org>
Date:   Mon, 31 Jan 2022 11:54:59 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.15 034/171] KVM: LAPIC: Also cancel preemption timer during SET_LAPIC

From: Wanpeng Li <wanpengli@...cent.com>

commit 35fe7cfbab2e81f1afb23fc4212210b1de6d9633 upstream.

The below warning is splatting during guest reboot.

  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 1931 at arch/x86/kvm/x86.c:10322 kvm_arch_vcpu_ioctl_run+0x874/0x880 [kvm]
  CPU: 0 PID: 1931 Comm: qemu-system-x86 Tainted: G          I       5.17.0-rc1+ #5
  RIP: 0010:kvm_arch_vcpu_ioctl_run+0x874/0x880 [kvm]
  Call Trace:
   <TASK>
   kvm_vcpu_ioctl+0x279/0x710 [kvm]
   __x64_sys_ioctl+0x83/0xb0
   do_syscall_64+0x3b/0xc0
   entry_SYSCALL_64_after_hwframe+0x44/0xae
  RIP: 0033:0x7fd39797350b

This can be triggered by not exposing tsc-deadline mode and doing a reboot in
the guest. The lapic_shutdown() function which is called in sys_reboot path
will not disarm the flying timer, it just masks LVTT. lapic_shutdown() clears
APIC state w/ LVT_MASKED and timer-mode bit is 0, this can trigger timer-mode
switch between tsc-deadline and oneshot/periodic, which can result in preemption
timer be cancelled in apic_update_lvtt(). However, We can't depend on this when
not exposing tsc-deadline mode and oneshot/periodic modes emulated by preemption
timer. Qemu will synchronise states around reset, let's cancel preemption timer
under KVM_SET_LAPIC.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
Message-Id: <1643102220-35667-1-git-send-email-wanpengli@...cent.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/lapic.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2623,7 +2623,7 @@ int kvm_apic_set_state(struct kvm_vcpu *
 	kvm_apic_set_version(vcpu);
 
 	apic_update_ppr(apic);
-	hrtimer_cancel(&apic->lapic_timer.timer);
+	cancel_apic_timer(apic);
 	apic->lapic_timer.expired_tscdeadline = 0;
 	apic_update_lvtt(apic);
 	apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));