linux-kernel - [PATCH 07/19] KVM: SVM: Drop buggy and redundant AVIC "single logical dest" check

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Date:   Wed, 31 Aug 2022 00:34:54 +0000
From:   Sean Christopherson <seanjc@...gle.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>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Li RongQing <lirongqing@...du.com>
Subject: [PATCH 07/19] KVM: SVM: Drop buggy and redundant AVIC "single logical
 dest" check

Use the already-calculated-and-sanity-checked destination bitmap when
processing a fast AVIC kick in logical mode, and drop the logical path's
flawed logic.  The intent of the check is to ensure the bitmap is a power
of two, whereas "icrh != (1 << avic)" effectively checks that the bitmap
is a power of two _and_ the target cluster is '0'.

Note, the flawed check isn't a functional issue, it simply means that KVM
will go down the slow path if the target cluster is non-zero.

Fixes: 8c9e639da435 ("KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/avic.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 3c333cd2e752..14f567550a1e 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -411,15 +411,7 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 			 * Instead, calculate physical ID from logical ID in ICRH.
 			 */
 			int cluster = (icrh & 0xffff0000) >> 16;
-			int apic = ffs(icrh & 0xffff) - 1;
-
-			/*
-			 * If the x2APIC logical ID sub-field (i.e. icrh[15:0])
-			 * contains anything but a single bit, we cannot use the
-			 * fast path, because it is limited to a single vCPU.
-			 */
-			if (apic < 0 || icrh != (1 << apic))
-				return -EINVAL;
+			int apic = ffs(bitmap) - 1;
 
 			l1_physical_id = (cluster << 4) + apic;
 		}
-- 
2.37.2.672.g94769d06f0-goog