KVM: VMX: Consume pending LAPIC INIT event when exit on INIT_SIGNAL
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Message ID 20191111121605.92972-1-liran.alon@oracle.com
State New
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  • KVM: VMX: Consume pending LAPIC INIT event when exit on INIT_SIGNAL
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Commit Message

Liran Alon Nov. 11, 2019, 12:16 p.m. UTC
Intel SDM section 25.2 OTHER CAUSES OF VM EXITS specifies the following
on INIT signals: "Such exits do not modify register state or clear pending
events as they would outside of VMX operation."

When commit 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
was applied, I interepted above Intel SDM statement such that
INIT_SIGNAL exit don’t consume the LAPIC INIT pending event.

However, when Nadav Amit run matching kvm-unit-test on a bare-metal
machine, it turned out my interpetation was wrong. i.e. INIT_SIGNAL
exit does consume the LAPIC INIT pending event.
(See: https://www.spinics.net/lists/kvm/msg196757.html)

Therefore, fix KVM code to behave as observed on bare-metal.

Fixes: 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
Reported-by: Nadav Amit <nadav.amit@gmail.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
---
 arch/x86/kvm/vmx/nested.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Paolo Bonzini Nov. 13, 2019, 3:24 p.m. UTC | #1
On 11/11/19 13:16, Liran Alon wrote:
> Intel SDM section 25.2 OTHER CAUSES OF VM EXITS specifies the following
> on INIT signals: "Such exits do not modify register state or clear pending
> events as they would outside of VMX operation."
> 
> When commit 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
> was applied, I interepted above Intel SDM statement such that
> INIT_SIGNAL exit don’t consume the LAPIC INIT pending event.
> 
> However, when Nadav Amit run matching kvm-unit-test on a bare-metal
> machine, it turned out my interpetation was wrong. i.e. INIT_SIGNAL
> exit does consume the LAPIC INIT pending event.
> (See: https://www.spinics.net/lists/kvm/msg196757.html)
> 
> Therefore, fix KVM code to behave as observed on bare-metal.
> 
> Fixes: 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
> Reported-by: Nadav Amit <nadav.amit@gmail.com>
> Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
> Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 0e7c9301fe86..2c4336ac7576 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3461,6 +3461,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>  		test_bit(KVM_APIC_INIT, &apic->pending_events)) {
>  		if (block_nested_events)
>  			return -EBUSY;
> +		clear_bit(KVM_APIC_INIT, &apic->pending_events);
>  		nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
>  		return 0;
>  	}
> 

Queued, thanks.

Paolo
Paolo Bonzini Nov. 15, 2019, 10:20 a.m. UTC | #2
On 11/11/19 13:16, Liran Alon wrote:
> Intel SDM section 25.2 OTHER CAUSES OF VM EXITS specifies the following
> on INIT signals: "Such exits do not modify register state or clear pending
> events as they would outside of VMX operation."
> 
> When commit 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
> was applied, I interepted above Intel SDM statement such that
> INIT_SIGNAL exit don’t consume the LAPIC INIT pending event.
> 
> However, when Nadav Amit run matching kvm-unit-test on a bare-metal
> machine, it turned out my interpetation was wrong. i.e. INIT_SIGNAL
> exit does consume the LAPIC INIT pending event.
> (See: https://www.spinics.net/lists/kvm/msg196757.html)
> 
> Therefore, fix KVM code to behave as observed on bare-metal.
> 
> Fixes: 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
> Reported-by: Nadav Amit <nadav.amit@gmail.com>
> Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
> Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 0e7c9301fe86..2c4336ac7576 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3461,6 +3461,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>  		test_bit(KVM_APIC_INIT, &apic->pending_events)) {
>  		if (block_nested_events)
>  			return -EBUSY;
> +		clear_bit(KVM_APIC_INIT, &apic->pending_events);
>  		nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
>  		return 0;
>  	}
> 

Queued, thanks.

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0e7c9301fe86..2c4336ac7576 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3461,6 +3461,7 @@  static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
 		test_bit(KVM_APIC_INIT, &apic->pending_events)) {
 		if (block_nested_events)
 			return -EBUSY;
+		clear_bit(KVM_APIC_INIT, &apic->pending_events);
 		nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
 		return 0;
 	}