For VMX, when a vcpu enters HLT emulation, pi_post_block will:
1) Add vcpu to per-cpu list of blocked vcpus.
2) Program the posted-interrupt descriptor "notification vector"
to POSTED_INTR_WAKEUP_VECTOR
With interrupt remapping, an interrupt will set the PIR bit for the
vector programmed for the device on the CPU, test-and-set the
ON bit on the posted interrupt descriptor, and if the ON bit is clear
generate an interrupt for the notification vector.
This way, the target CPU wakes upon a device interrupt and wakes up
the target vcpu.
Problem is that pi_post_block only programs the notification vector
if kvm_arch_has_assigned_device() is true. Its possible for the
following to happen:
1) vcpu V HLTs on pcpu P, kvm_arch_has_assigned_device is false,
notification vector is not programmed
2) device is assigned to VM
3) device interrupts vcpu V, sets ON bit (notification vector not programmed,
so pcpu P remains in idle)
4) vcpu 0 IPIs vcpu V (in guest), but since pi descriptor ON bit is set,
kvm_vcpu_kick is skipped
5) vcpu 0 busy spins on vcpu V's response for several seconds, until
RCU watchdog NMIs all vCPUs.
To fix this, use the start_assignment kvm_x86_ops callback to program the
notification vector when assigned device count changes from 0 to 1.
Reported-by: Pei Zhang <pezhang@xxxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
---
v2: add vmx_pi_start_assignment to vmx's kvm_x86_ops
Index: kvm/arch/x86/kvm/vmx/posted_intr.c
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/posted_intr.c
+++ kvm/arch/x86/kvm/vmx/posted_intr.c
@@ -114,7 +114,7 @@ static void __pi_post_block(struct kvm_v
} while (cmpxchg64(&pi_desc->control, old.control,
new.control) != old.control);
- if (!WARN_ON_ONCE(vcpu->pre_pcpu == -1)) {
+ if (vcpu->pre_pcpu != -1) {
spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
list_del(&vcpu->blocked_vcpu_list);
spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
@@ -135,20 +135,13 @@ static void __pi_post_block(struct kvm_v
* this case, return 1, otherwise, return 0.
*
*/
-int pi_pre_block(struct kvm_vcpu *vcpu)
+static int __pi_pre_block(struct kvm_vcpu *vcpu)
{
unsigned int dest;
struct pi_desc old, new;
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
- if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
- !irq_remapping_cap(IRQ_POSTING_CAP) ||
- !kvm_vcpu_apicv_active(vcpu))
- return 0;
-
- WARN_ON(irqs_disabled());
- local_irq_disable();
- if (!WARN_ON_ONCE(vcpu->pre_pcpu != -1)) {
+ if (vcpu->pre_pcpu == -1) {
vcpu->pre_pcpu = vcpu->cpu;
spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
list_add_tail(&vcpu->blocked_vcpu_list,
@@ -188,12 +181,33 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
if (pi_test_on(pi_desc) == 1)
__pi_post_block(vcpu);
+ return (vcpu->pre_pcpu == -1);
+}
+
+int pi_pre_block(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ vmx->in_blocked_section = true;
+
+ if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
+ !irq_remapping_cap(IRQ_POSTING_CAP) ||
+ !kvm_vcpu_apicv_active(vcpu))
+ return 0;
+
+ WARN_ON(irqs_disabled());
+ local_irq_disable();
+ __pi_pre_block(vcpu);
local_irq_enable();
+
return (vcpu->pre_pcpu == -1);
}
void pi_post_block(struct kvm_vcpu *vcpu)
{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ vmx->in_blocked_section = false;
if (vcpu->pre_pcpu == -1)
return;
@@ -236,6 +250,52 @@ bool pi_has_pending_interrupt(struct kvm
(pi_test_sn(pi_desc) && !pi_is_pir_empty(pi_desc));
}
+static void pi_update_wakeup_vector(void *data)
+{
+ struct vcpu_vmx *vmx;
+ struct kvm_vcpu *vcpu = data;
+
+ vmx = to_vmx(vcpu);
+
+ /* race with pi_post_block ? */
+ if (vcpu->pre_pcpu != -1)
+ return;
+
+ if (!vmx->in_blocked_section)
+ return;
+
+ __pi_pre_block(vcpu);
+}
+
+void vmx_pi_start_assignment(struct kvm *kvm, int device_count)
+{
+ struct kvm_vcpu *vcpu;
+ int i;
+
+ if (!irq_remapping_cap(IRQ_POSTING_CAP))
+ return;
+
+ /* only care about first device assignment */
+ if (device_count != 1)
+ return;
+
+ /* Update wakeup vector and add vcpu to blocked_vcpu_list */
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ int pcpu;
+
+ if (!kvm_vcpu_apicv_active(vcpu))
+ continue;
+
+ preempt_disable();
+ pcpu = vcpu->cpu;
+ if (vmx->in_blocked_section && vcpu->pre_pcpu == -1 &&
+ pcpu != -1 && pcpu != smp_processor_id())
+ smp_call_function_single(pcpu, pi_update_wakeup_vector,
+ vcpu, 1);
+ preempt_enable();
+ }
+}
/*
* pi_update_irte - set IRTE for Posted-Interrupts
Index: kvm/arch/x86/kvm/vmx/posted_intr.h
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/posted_intr.h
+++ kvm/arch/x86/kvm/vmx/posted_intr.h
@@ -95,5 +95,6 @@ void __init pi_init_cpu(int cpu);
bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu);
int pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq,
bool set);
+void vmx_pi_start_assignment(struct kvm *kvm, int device_count);
#endif /* __KVM_X86_VMX_POSTED_INTR_H */
Index: kvm/arch/x86/kvm/vmx/vmx.h
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/vmx.h
+++ kvm/arch/x86/kvm/vmx/vmx.h
@@ -336,6 +336,9 @@ struct vcpu_vmx {
DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
} shadow_msr_intercept;
+
+ /* true if vcpu is between pre_block and post_block */
+ bool in_blocked_section;
};
enum ept_pointers_status {
Index: kvm/arch/x86/kvm/vmx/vmx.c
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/vmx.c
+++ kvm/arch/x86/kvm/vmx/vmx.c
@@ -7732,7 +7732,7 @@ static struct kvm_x86_ops vmx_x86_ops __
.nested_ops = &vmx_nested_ops,
.update_pi_irte = pi_update_irte,
- .start_assignment = NULL,
+ .start_assignment = vmx_pi_start_assignment,
#ifdef CONFIG_X86_64
.set_hv_timer = vmx_set_hv_timer,
