We can interrupt the vcpu only when it's running in guest mode
to reduce IPI
It looks like only ia64 and x86 need to send IPI to other vcpus, so
i only add the implementation of 'vcpu->guest_mode' in ia64, but i
don't know ia64 well, please point out the right way for me if the
implementation is incorrect
Also reorganize struct kvm_vcpu to make ->guest_mode and ->requests
in the same cache line explicitly.
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
arch/ia64/kvm/kvm-ia64.c | 2 ++
arch/x86/kvm/x86.c | 6 +++++-
include/linux/kvm_host.h | 9 +++++----
virt/kvm/kvm_main.c | 7 ++++++-
4 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 70d224d..15c11b2 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -662,6 +662,7 @@ again:
goto vcpu_run_fail;
srcu_read_unlock(&vcpu->kvm->srcu, idx);
+ atomic_set(&vcpu->guest_mode, 1);
kvm_guest_enter();
/*
@@ -683,6 +684,7 @@ again:
*/
barrier();
kvm_guest_exit();
+ atomic_set(&vcpu->guest_mode, 0);
preempt_enable();
idx = srcu_read_lock(&vcpu->kvm->srcu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0b77e9c..f882158 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5214,7 +5214,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_load_guest_xcr0(vcpu);
atomic_set(&vcpu->guest_mode, 1);
- smp_wmb();
+
+ /* We should set ->guest_mode before check ->requests,
+ * see the comment in make_all_cpus_request.
+ */
+ smp_mb();
local_irq_disable();
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b5021db..5f5ef74 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -103,14 +103,15 @@ struct kvm_vcpu {
#ifdef CONFIG_PREEMPT_NOTIFIERS
struct preempt_notifier preempt_notifier;
#endif
+ int cpu;
int vcpu_id;
- struct mutex mutex;
- int cpu;
+ int srcu_idx;
atomic_t guest_mode;
- struct kvm_run *run;
unsigned long requests;
unsigned long guest_debug;
- int srcu_idx;
+
+ struct mutex mutex;
+ struct kvm_run *run;
int fpu_active;
int guest_fpu_loaded, guest_xcr0_loaded;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b1b6cbb..a475264 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -153,7 +153,12 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
if (kvm_make_check_request(req, vcpu))
continue;
cpu = vcpu->cpu;
- if (cpus != NULL && cpu != -1 && cpu != me)
+
+ /* Set ->requests bit before we read ->guest_mode */
+ smp_mb();
+
+ if (cpus != NULL && cpu != -1 && cpu != me &&
+ atomic_read(&vcpu->guest_mode))
cpumask_set_cpu(cpu, cpus);
}
if (unlikely(cpus == NULL))
--
1.7.3.4
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