Re: [PATCH 65/67] KVM: SVM: Generate GA log IRQs only if the associated vCPUs is blocking
From: Sean Christopherson
Date: Tue Apr 08 2025 - 17:31:40 EST
On Tue, Apr 08, 2025, Paolo Bonzini wrote:
> On 4/4/25 21:39, Sean Christopherson wrote:
> > @@ -892,7 +893,7 @@ static void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu, bool toggle_avic)
> > WRITE_ONCE(kvm_svm->avic_physical_id_table[vcpu->vcpu_id], entry);
> > - avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, toggle_avic);
> > + avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, toggle_avic, false);
> > spin_unlock_irqrestore(&svm->ir_list_lock, flags);
> > }
> > @@ -912,7 +913,8 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> > __avic_vcpu_load(vcpu, cpu, false);
> > }
> > -static void __avic_vcpu_put(struct kvm_vcpu *vcpu, bool toggle_avic)
> > +static void __avic_vcpu_put(struct kvm_vcpu *vcpu, bool toggle_avic,
> > + bool is_blocking)
>
> What would it look like to use an enum { SCHED_OUT, SCHED_IN, ENABLE_AVIC,
> DISABLE_AVIC, START_BLOCKING } for both __avic_vcpu_put and
> __avic_vcpu_load's second argument?
There's gotta be a way to make it look better than this code. I gave a half-
hearted attempt at using an enum before posting, but wasn't able to come up with
anything decent.
Coming back to it with fresh eyes, what about this (full on-top diff below)?
enum avic_vcpu_action {
AVIC_SCHED_IN = 0,
AVIC_SCHED_OUT = 0,
AVIC_START_BLOCKING = BIT(0),
AVIC_TOGGLE_ON_OFF = BIT(1),
AVIC_ACTIVATE = AVIC_TOGGLE_ON_OFF,
AVIC_DEACTIVATE = AVIC_TOGGLE_ON_OFF,
};
AVIC_SCHED_IN and AVIC_SCHED_OUT are essentially syntactic sugar, as are
AVIC_ACTIVATE and AVIC_DEACTIVATE to a certain extent. But it's much better than
booleans, and using a bitmask makes avic_update_iommu_vcpu_affinity() slightly
prettier.
> Consecutive bools are ugly...
Yeah, I hated it when I wrote it, and still hate it now.
And more error prone, e.g. the __avic_vcpu_put() call from avic_refresh_apicv_exec_ctrl()
should specify is_blocking=false, not true, as kvm_x86_ops.refresh_apicv_exec_ctrl()
should never be called while the vCPU is blocking.
---
arch/x86/kvm/svm/avic.c | 41 ++++++++++++++++++++++++++++-------------
1 file changed, 28 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 425674e1a04c..1752420c68aa 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -833,9 +833,20 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
return irq_set_vcpu_affinity(host_irq, NULL);
}
+enum avic_vcpu_action {
+ AVIC_SCHED_IN = 0,
+ AVIC_SCHED_OUT = 0,
+ AVIC_START_BLOCKING = BIT(0),
+
+ AVIC_TOGGLE_ON_OFF = BIT(1),
+ AVIC_ACTIVATE = AVIC_TOGGLE_ON_OFF,
+ AVIC_DEACTIVATE = AVIC_TOGGLE_ON_OFF,
+};
+
static void avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu,
- bool toggle_avic, bool ga_log_intr)
+ enum avic_vcpu_action action)
{
+ bool ga_log_intr = (action & AVIC_START_BLOCKING);
struct amd_svm_iommu_ir *ir;
struct vcpu_svm *svm = to_svm(vcpu);
@@ -849,7 +860,7 @@ static void avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu,
return;
list_for_each_entry(ir, &svm->ir_list, node) {
- if (!toggle_avic)
+ if (!(action & AVIC_TOGGLE_ON_OFF))
WARN_ON_ONCE(amd_iommu_update_ga(ir->data, cpu, ga_log_intr));
else if (cpu >= 0)
WARN_ON_ONCE(amd_iommu_activate_guest_mode(ir->data, cpu, ga_log_intr));
@@ -858,7 +869,8 @@ static void avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu,
}
}
-static void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu, bool toggle_avic)
+static void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu,
+ enum avic_vcpu_action action)
{
struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
int h_physical_id = kvm_cpu_get_apicid(cpu);
@@ -904,7 +916,7 @@ static void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu, bool toggle_avic)
WRITE_ONCE(kvm_svm->avic_physical_id_table[vcpu->vcpu_id], entry);
- avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, toggle_avic, false);
+ avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, action);
spin_unlock_irqrestore(&svm->ir_list_lock, flags);
}
@@ -921,11 +933,10 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
if (kvm_vcpu_is_blocking(vcpu))
return;
- __avic_vcpu_load(vcpu, cpu, false);
+ __avic_vcpu_load(vcpu, cpu, AVIC_SCHED_IN);
}
-static void __avic_vcpu_put(struct kvm_vcpu *vcpu, bool toggle_avic,
- bool is_blocking)
+static void __avic_vcpu_put(struct kvm_vcpu *vcpu, enum avic_vcpu_action action)
{
struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
struct vcpu_svm *svm = to_svm(vcpu);
@@ -947,7 +958,7 @@ static void __avic_vcpu_put(struct kvm_vcpu *vcpu, bool toggle_avic,
*/
spin_lock_irqsave(&svm->ir_list_lock, flags);
- avic_update_iommu_vcpu_affinity(vcpu, -1, toggle_avic, is_blocking);
+ avic_update_iommu_vcpu_affinity(vcpu, -1, action);
WARN_ON_ONCE(entry & AVIC_PHYSICAL_ID_ENTRY_GA_LOG_INTR);
@@ -964,7 +975,7 @@ static void __avic_vcpu_put(struct kvm_vcpu *vcpu, bool toggle_avic,
* Note! Don't set AVIC_PHYSICAL_ID_ENTRY_GA_LOG_INTR in the table as
* it's a synthetic flag that usurps an unused a should-be-zero bit.
*/
- if (is_blocking)
+ if (action & AVIC_START_BLOCKING)
entry |= AVIC_PHYSICAL_ID_ENTRY_GA_LOG_INTR;
svm->avic_physical_id_entry = entry;
@@ -992,7 +1003,8 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
return;
}
- __avic_vcpu_put(vcpu, false, kvm_vcpu_is_blocking(vcpu));
+ __avic_vcpu_put(vcpu, kvm_vcpu_is_blocking(vcpu) ? AVIC_START_BLOCKING :
+ AVIC_SCHED_OUT);
}
void avic_refresh_virtual_apic_mode(struct kvm_vcpu *vcpu)
@@ -1024,12 +1036,15 @@ void avic_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
if (!enable_apicv)
return;
+ /* APICv should only be toggled on/off while the vCPU is running. */
+ WARN_ON_ONCE(kvm_vcpu_is_blocking(vcpu));
+
avic_refresh_virtual_apic_mode(vcpu);
if (kvm_vcpu_apicv_active(vcpu))
- __avic_vcpu_load(vcpu, vcpu->cpu, true);
+ __avic_vcpu_load(vcpu, vcpu->cpu, AVIC_ACTIVATE);
else
- __avic_vcpu_put(vcpu, true, true);
+ __avic_vcpu_put(vcpu, AVIC_DEACTIVATE);
}
void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
@@ -1055,7 +1070,7 @@ void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
* CPU and cause noisy neighbor problems if the VM is sending interrupts
* to the vCPU while it's scheduled out.
*/
- __avic_vcpu_put(vcpu, false, true);
+ __avic_vcpu_put(vcpu, AVIC_START_BLOCKING);
}
void avic_vcpu_unblocking(struct kvm_vcpu *vcpu)
base-commit: fe5b44cf46d5444ff071bc2373fbe7b109a3f60b
--