[PATCH v3 13/26] KVM: SVM: Use kvm_vcpu_is_blocking() in AVIC load to handle preemption

Sean Christopherson
2021-12-08T01:55:31Z

Use kvm_vcpu_is_blocking() to determine whether or not the vCPU should be
marked running during avic_vcpu_load(). Drop avic_is_running, which
really should have been named "vcpu_is_not_blocking", as it tracked if
the vCPU was blocking, not if it was actually running, e.g. it was set
during svm_create_vcpu() when the vCPU was obviously not running.

This is technically a teeny tiny functional change, as the vCPU will be
marked IsRunning=1 on being reloaded if the vCPU is preempted between
svm_vcpu_blocking() and prepare_to_rcuwait(). But that's a benign change
as the vCPU will be marked IsRunning=0 when KVM voluntarily schedules out
the vCPU.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/avic.c | 14 +++++++++-----
arch/x86/kvm/svm/svm.c | 6 ------
arch/x86/kvm/svm/svm.h | 1 -
3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 16e4ebd980a2..dc0cbe500106 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -974,6 +974,7 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
u64 entry;
/* ID = 0xff (broadcast), ID > 0xff (reserved) */
+ bool is_blocking = kvm_vcpu_is_blocking(vcpu);
int h_physical_id = kvm_cpu_get_apicid(cpu);
struct vcpu_svm *svm = to_svm(vcpu);

@@ -991,12 +992,17 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
entry |= (h_physical_id & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK);

entry &= ~AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
- if (svm->avic_is_running)
+
+ /*
+ * Don't mark the vCPU as running if its blocking, i.e. if the vCPU is
+ * preempted after svm_vcpu_blocking() but before KVM voluntarily
+ * schedules out the vCPU.
+ */
+ if (!is_blocking)
entry |= AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;

WRITE_ONCE(*(svm->avic_physical_id_cache), entry);
- avic_update_iommu_vcpu_affinity(vcpu, h_physical_id,
- svm->avic_is_running);
+ avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, !is_blocking);
}

void avic_vcpu_put(struct kvm_vcpu *vcpu)
@@ -1017,11 +1023,9 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
*/
static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)
{
- struct vcpu_svm *svm = to_svm(vcpu);
int cpu = get_cpu();

WARN_ON(cpu != vcpu->cpu);
- svm->avic_is_running = is_run;

if (kvm_vcpu_apicv_active(vcpu)) {
if (is_run)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 208566f63bce..dde0106ffc47 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1444,12 +1444,6 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
if (err)
goto error_free_vmsa_page;

- /* We initialize this flag to true to make sure that the is_running
- * bit would be set the first time the vcpu is loaded.
- */
- if (irqchip_in_kernel(vcpu->kvm) && kvm_apicv_activated(vcpu->kvm))
- svm->avic_is_running = true;
-
svm->msrpm = svm_vcpu_alloc_msrpm();
if (!svm->msrpm) {
err = -ENOMEM;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ca51d6dfc8e6..83ced47fa9b9 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -226,7 +226,6 @@ struct vcpu_svm {
u32 dfr_reg;
struct page *avic_backing_page;
u64 *avic_physical_id_cache;
- bool avic_is_running;

/*
* Per-vcpu list of struct amd_svm_iommu_ir:
--
2.34.1.400.ga245620fadb-goog