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authorChristoffer Dall <cdall@linaro.org>2016-10-16 20:30:38 +0200
committerChristoffer Dall <christoffer.dall@linaro.org>2017-11-06 16:23:14 +0100
commitb103cc3f10c06fb81faacd4ee6f88bbd21246073 (patch)
treeb5be5218359c1dc8c1a570683dfe2ae917b57ba3 /include/kvm
parent40f4cba9a579fe7ad1431269db8aec745c290ba0 (diff)
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KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit
We don't need to save and restore the hardware timer state and examine if it generates interrupts on on every entry/exit to the guest. The timer hardware is perfectly capable of telling us when it has expired by signaling interrupts. When taking a vtimer interrupt in the host, we don't want to mess with the timer configuration, we just want to forward the physical interrupt to the guest as a virtual interrupt. We can use the split priority drop and deactivate feature of the GIC to do this, which leaves an EOI'ed interrupt active on the physical distributor, making sure we don't keep taking timer interrupts which would prevent the guest from running. We can then forward the physical interrupt to the VM using the HW bit in the LR of the GIC, like we do already, which lets the guest directly deactivate both the physical and virtual timer simultaneously, allowing the timer hardware to exit the VM and generate a new physical interrupt when the timer output is again asserted later on. We do need to capture this state when migrating VCPUs between physical CPUs, however, which we use the vcpu put/load functions for, which are called through preempt notifiers whenever the thread is scheduled away from the CPU or called directly if we return from the ioctl to userspace. One caveat is that we have to save and restore the timer state in both kvm_timer_vcpu_[put/load] and kvm_timer_[schedule/unschedule], because we can have the following flows: 1. kvm_vcpu_block 2. kvm_timer_schedule 3. schedule 4. kvm_timer_vcpu_put (preempt notifier) 5. schedule (vcpu thread gets scheduled back) 6. kvm_timer_vcpu_load (preempt notifier) 7. kvm_timer_unschedule And a version where we don't actually call schedule: 1. kvm_vcpu_block 2. kvm_timer_schedule 7. kvm_timer_unschedule Since kvm_timer_[schedule/unschedule] may not be followed by put/load, but put/load also may be called independently, we call the timer save/restore functions from both paths. Since they rely on the loaded flag to never save/restore when unnecessary, this doesn't cause any harm, and we ensure that all invokations of either set of functions work as intended. An added benefit beyond not having to read and write the timer sysregs on every entry and exit is that we no longer have to actively write the active state to the physical distributor, because we configured the irq for the vtimer to only get a priority drop when handling the interrupt in the GIC driver (we called irq_set_vcpu_affinity()), and the interrupt stays active after firing on the host. Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <cdall@linaro.org>
Diffstat (limited to 'include/kvm')
-rw-r--r--include/kvm/arm_arch_timer.h16
1 files changed, 14 insertions, 2 deletions
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index 184c3ef2df93..c538f707e1c1 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -31,8 +31,15 @@ struct arch_timer_context {
/* Timer IRQ */
struct kvm_irq_level irq;
- /* Active IRQ state caching */
- bool active_cleared_last;
+ /*
+ * We have multiple paths which can save/restore the timer state
+ * onto the hardware, so we need some way of keeping track of
+ * where the latest state is.
+ *
+ * loaded == true: State is loaded on the hardware registers.
+ * loaded == false: State is stored in memory.
+ */
+ bool loaded;
/* Virtual offset */
u64 cntvoff;
@@ -78,10 +85,15 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu);
u64 kvm_phys_timer_read(void);
+void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu);
void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu);
void kvm_timer_init_vhe(void);
#define vcpu_vtimer(v) (&(v)->arch.timer_cpu.vtimer)
#define vcpu_ptimer(v) (&(v)->arch.timer_cpu.ptimer)
+
+void enable_el1_phys_timer_access(void);
+void disable_el1_phys_timer_access(void);
+
#endif