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Message-ID: <4a4bc3ad639b0dca9f24a7616d86a7cc9abd13ea.camel@redhat.com>
Date: Wed, 31 Aug 2022 16:24:34 +0300
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH 13/19] KVM: x86: Disable APIC logical map if vCPUs are
aliased in logical mode
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@...gle.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@...hat.com>
Best regards,
Maxim Levitsky
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