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KVM: arm/arm64: Simplify bg_timer programming 

Instead of calling into kvm_timer_[un]schedule from the main kvm
blocking path, test if the VCPU is on the wait queue from the load/put
path and perform the background timer setup/cancel in this path.

This has the distinct advantage that we no longer race between load/put
and schedule/unschedule and programming and canceling of the bg_timer
always happens when the timer state is not loaded.

Note that we must now remove the checks in kvm_timer_blocking that do
not schedule a background timer if one of the timers can fire, because
we no longer have a guarantee that kvm_vcpu_check_block() will be called
before kvm_timer_blocking.

Reported-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
This commit is contained in:
Christoffer Dall 2018-11-26 18:21:22 +01:00 committed by Marc Zyngier
parent e329fb75d5
commit accb99bcd0
3 changed files with 14 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/kvm/arm_arch_timer.h
View File

@ -76,9 +76,6 @@ int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr);
bool kvm_timer_is_pending(struct kvm_vcpu *vcpu);
void kvm_timer_schedule(struct kvm_vcpu *vcpu);
void kvm_timer_unschedule(struct kvm_vcpu *vcpu);
u64 kvm_phys_timer_read(void);
void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu);

35
virt/kvm/arm/arch_timer.c
View File

@ -349,22 +349,12 @@ static void vtimer_save_state(struct kvm_vcpu *vcpu)
* thread is removed from its waitqueue and made runnable when there's a timer
* interrupt to handle.
*/
void kvm_timer_schedule(struct kvm_vcpu *vcpu)
static void kvm_timer_blocking(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
vtimer_save_state(vcpu);
/*
* No need to schedule a background timer if any guest timer has
* already expired, because kvm_vcpu_block will return before putting
* the thread to sleep.
*/
if (kvm_timer_should_fire(vtimer) || kvm_timer_should_fire(ptimer))
return;
/*
* If both timers are not capable of raising interrupts (disabled or
* masked), then there's no more work for us to do.
@ -373,12 +363,19 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
return;
/*
* The guest timers have not yet expired, schedule a background timer.
* At least one guest time will expire. Schedule a background timer.
* Set the earliest expiration time among the guest timers.
*/
soft_timer_start(&timer->bg_timer, kvm_timer_earliest_exp(vcpu));
}
static void kvm_timer_unblocking(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
soft_timer_cancel(&timer->bg_timer);
}
static void vtimer_restore_state(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
@ -401,15 +398,6 @@ static void vtimer_restore_state(struct kvm_vcpu *vcpu)
local_irq_restore(flags);
}
void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
vtimer_restore_state(vcpu);
soft_timer_cancel(&timer->bg_timer);
}
static void set_cntvoff(u64 cntvoff)
{
u32 low = lower_32_bits(cntvoff);
@ -485,6 +473,8 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
/* Set the background timer for the physical timer emulation. */
phys_timer_emulate(vcpu);
kvm_timer_unblocking(vcpu);
/* If the timer fired while we weren't running, inject it now */
if (kvm_timer_should_fire(ptimer) != ptimer->irq.level)
kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer);
@ -527,6 +517,9 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
*/
soft_timer_cancel(&timer->phys_timer);
if (swait_active(kvm_arch_vcpu_wq(vcpu)))
kvm_timer_blocking(vcpu);
/*
* The kernel may decide to run userspace after calling vcpu_put, so
* we reset cntvoff to 0 to ensure a consistent read between user

2
virt/kvm/arm/arm.c
View File

@ -335,13 +335,11 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
{
kvm_timer_schedule(vcpu);
kvm_vgic_v4_enable_doorbell(vcpu);
}
void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
{
kvm_timer_unschedule(vcpu);
kvm_vgic_v4_disable_doorbell(vcpu);
}