[v1] KVM: x86: AVIC and local APIC fixes+cleanups

[PATCH 13/19] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode

Posted by Sean Christopherson 3 years, 7 months ago

Disable the optimized APIC logical map if multiple vCPUs are aliased to
the same logical ID.  Architecturally, all CPUs whose logical ID matches
the MDA are supposed to receive the interrupt; overwriting existing map
entries can result in missed IPIs.

Fixes: 1e08ec4a130e ("KVM: optimize apic interrupt delivery")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 82278acae95b..d537b51295d6 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -303,12 +303,13 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
 		if (!mask)
 			continue;
 
-		if (!is_power_of_2(mask)) {
+		ldr = ffs(mask) - 1;
+		if (!is_power_of_2(mask) || cluster[ldr]) {
 			new->mode = KVM_APIC_MODE_XAPIC_FLAT |
 				    KVM_APIC_MODE_XAPIC_CLUSTER;
 			continue;
 		}
-		cluster[ffs(mask) - 1] = apic;
+		cluster[ldr] = apic;
 	}
 out:
 	old = rcu_dereference_protected(kvm->arch.apic_map,
-- 
2.37.2.672.g94769d06f0-goog

Re: [PATCH 13/19] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode

Posted by Maxim Levitsky 3 years, 7 months ago

On Wed, 2022-08-31 at 00:35 +0000, Sean Christopherson wrote:
> Disable the optimized APIC logical map if multiple vCPUs are aliased to
> the same logical ID.  Architecturally, all CPUs whose logical ID matches
> the MDA are supposed to receive the interrupt; overwriting existing map
> entries can result in missed IPIs.
> 
> Fixes: 1e08ec4a130e ("KVM: optimize apic interrupt delivery")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/lapic.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 82278acae95b..d537b51295d6 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -303,12 +303,13 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
>  		if (!mask)
>  			continue;
>  
> -		if (!is_power_of_2(mask)) {
> +		ldr = ffs(mask) - 1;
> +		if (!is_power_of_2(mask) || cluster[ldr]) {
>  			new->mode = KVM_APIC_MODE_XAPIC_FLAT |
>  				    KVM_APIC_MODE_XAPIC_CLUSTER;
>  			continue;
>  		}
> -		cluster[ffs(mask) - 1] = apic;
> +		cluster[ldr] = apic;
>  	}
>  out:
>  	old = rcu_dereference_protected(kvm->arch.apic_map,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky