KVM: LAPIC: Fix reentrancy issues with preempt notifiers
Preempt can occur in the preemption timer expiration handler:
CPU0 CPU1
preemption timer vmexit
handle_preemption_timer(vCPU0)
kvm_lapic_expired_hv_timer
hv_timer_is_use == true
sched_out
sched_in
kvm_arch_vcpu_load
kvm_lapic_restart_hv_timer
restart_apic_timer
start_hv_timer
already-expired timer or sw timer triggerd in the window
start_sw_timer
cancel_hv_timer
/* back in kvm_lapic_expired_hv_timer */
cancel_hv_timer
WARN_ON(!apic->lapic_timer.hv_timer_in_use); ==> Oops
This can be reproduced if CONFIG_PREEMPT is enabled.
------------[ cut here ]------------
WARNING: CPU: 4 PID: 2972 at /home/kernel/linux/arch/x86/kvm//lapic.c:1563 kvm_lapic_expired_hv_timer+0x9e/0xb0 [kvm]
CPU: 4 PID: 2972 Comm: qemu-system-x86 Tainted: G OE 4.13.0-rc2+ #16
RIP: 0010:kvm_lapic_expired_hv_timer+0x9e/0xb0 [kvm]
Call Trace:
handle_preemption_timer+0xe/0x20 [kvm_intel]
vmx_handle_exit+0xb8/0xd70 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0xdd1/0x1be0 [kvm]
? kvm_arch_vcpu_load+0x47/0x230 [kvm]
? kvm_arch_vcpu_load+0x62/0x230 [kvm]
kvm_vcpu_ioctl+0x340/0x700 [kvm]
? kvm_vcpu_ioctl+0x340/0x700 [kvm]
? __fget+0xfc/0x210
do_vfs_ioctl+0xa4/0x6a0
? __fget+0x11d/0x210
SyS_ioctl+0x79/0x90
do_syscall_64+0x81/0x220
entry_SYSCALL64_slow_path+0x25/0x25
------------[ cut here ]------------
WARNING: CPU: 4 PID: 2972 at /home/kernel/linux/arch/x86/kvm//lapic.c:1498 cancel_hv_timer.isra.40+0x4f/0x60 [kvm]
CPU: 4 PID: 2972 Comm: qemu-system-x86 Tainted: G W OE 4.13.0-rc2+ #16
RIP: 0010:cancel_hv_timer.isra.40+0x4f/0x60 [kvm]
Call Trace:
kvm_lapic_expired_hv_timer+0x3e/0xb0 [kvm]
handle_preemption_timer+0xe/0x20 [kvm_intel]
vmx_handle_exit+0xb8/0xd70 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0xdd1/0x1be0 [kvm]
? kvm_arch_vcpu_load+0x47/0x230 [kvm]
? kvm_arch_vcpu_load+0x62/0x230 [kvm]
kvm_vcpu_ioctl+0x340/0x700 [kvm]
? kvm_vcpu_ioctl+0x340/0x700 [kvm]
? __fget+0xfc/0x210
do_vfs_ioctl+0xa4/0x6a0
? __fget+0x11d/0x210
SyS_ioctl+0x79/0x90
do_syscall_64+0x81/0x220
entry_SYSCALL64_slow_path+0x25/0x25
This patch fixes it by making the caller of cancel_hv_timer, start_hv_timer
and start_sw_timer be in preemption-disabled regions, which trivially
avoid any reentrancy issue with preempt notifier.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
[Add more WARNs. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2819d4c1..589dcc1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1495,11 +1495,10 @@
static void cancel_hv_timer(struct kvm_lapic *apic)
{
+ WARN_ON(preemptible());
WARN_ON(!apic->lapic_timer.hv_timer_in_use);
- preempt_disable();
kvm_x86_ops->cancel_hv_timer(apic->vcpu);
apic->lapic_timer.hv_timer_in_use = false;
- preempt_enable();
}
static bool start_hv_timer(struct kvm_lapic *apic)
@@ -1507,6 +1506,7 @@
struct kvm_timer *ktimer = &apic->lapic_timer;
int r;
+ WARN_ON(preemptible());
if (!kvm_x86_ops->set_hv_timer)
return false;
@@ -1538,6 +1538,8 @@
static void start_sw_timer(struct kvm_lapic *apic)
{
struct kvm_timer *ktimer = &apic->lapic_timer;
+
+ WARN_ON(preemptible());
if (apic->lapic_timer.hv_timer_in_use)
cancel_hv_timer(apic);
if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending))
@@ -1552,15 +1554,20 @@
static void restart_apic_timer(struct kvm_lapic *apic)
{
+ preempt_disable();
if (!start_hv_timer(apic))
start_sw_timer(apic);
+ preempt_enable();
}
void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
{
struct kvm_lapic *apic = vcpu->arch.apic;
- WARN_ON(!apic->lapic_timer.hv_timer_in_use);
+ preempt_disable();
+ /* If the preempt notifier has already run, it also called apic_timer_expired */
+ if (!apic->lapic_timer.hv_timer_in_use)
+ goto out;
WARN_ON(swait_active(&vcpu->wq));
cancel_hv_timer(apic);
apic_timer_expired(apic);
@@ -1569,6 +1576,8 @@
advance_periodic_target_expiration(apic);
restart_apic_timer(apic);
}
+out:
+ preempt_enable();
}
EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
@@ -1582,9 +1591,11 @@
{
struct kvm_lapic *apic = vcpu->arch.apic;
+ preempt_disable();
/* Possibly the TSC deadline timer is not enabled yet */
if (apic->lapic_timer.hv_timer_in_use)
start_sw_timer(apic);
+ preempt_enable();
}
EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);