Commit a2486020 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Paolo Bonzini
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KVM: VMX: update vcpu posted-interrupt descriptor when assigning device 



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 kick
vcpus out of the halt loop, so the notification vector is
properly reprogrammed to the wakeup vector.

Reported-by: default avatarPei Zhang <pezhang@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Message-Id: <20210526172014.GA29007@fuller.cnet>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 084071d5

arch/x86/kvm/vmx/posted_intr.c

+14 −0
Original line number Diff line number Diff line
@@ -237,6 +237,20 @@ bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu) 
}





/*

 * Bail out of the block loop if the VM has an assigned

 * device, but the blocking vCPU didn't reconfigure the

 * PI.NV to the wakeup vector, i.e. the assigned device

 * came along after the initial check in pi_pre_block().

 */

void vmx_pi_start_assignment(struct kvm *kvm)

{

	if (!irq_remapping_cap(IRQ_POSTING_CAP))

		return;



	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);

}



/*

 * pi_update_irte - set IRTE for Posted-Interrupts

 *

arch/x86/kvm/vmx/posted_intr.h

+1 −0
Original line number Diff line number Diff line
@@ -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);



#endif /* __KVM_X86_VMX_POSTED_INTR_H */

arch/x86/kvm/vmx/vmx.c

+1 −0
Original line number Diff line number Diff line
@@ -7721,6 +7721,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = { 
	.nested_ops = &vmx_nested_ops,



	.update_pi_irte = pi_update_irte,

	.start_assignment = vmx_pi_start_assignment,



#ifdef CONFIG_X86_64

	.set_hv_timer = vmx_set_hv_timer,

virt/kvm/kvm_main.c

+1 −0
Original line number Diff line number Diff line
@@ -307,6 +307,7 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req) 
{

	return kvm_make_all_cpus_request_except(kvm, req, NULL);

}

EXPORT_SYMBOL_GPL(kvm_make_all_cpus_request);



#ifndef CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL

void kvm_flush_remote_tlbs(struct kvm *kvm)