linux-kernel - [PATCH] KVM: SVM: Fix x2apic logical cluster mode decoding and sanity check

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Message-ID: <20220912214632.14880-1-suravee.suthikulpanit@amd.com>
Date:   Mon, 12 Sep 2022 16:46:32 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC:     <pbonzini@...hat.com>, <jon.grimm@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH] KVM: SVM: Fix x2apic logical cluster mode decoding and sanity check

When sending IPI in the X2APIC logical cluster mode, the destination
APIC ID is encoded as:

  * Cluster ID = ICRH[31:16]
  * Logical ID = ICRH[15:0]

Current logic incorrectly decode the ICRH, which causes VM running
with x2AVIC support to fail to boot. Therefore, fix the decoding logic.

The commit 603ccef42ce9 ("KVM: x86: SVM: fix avic_kick_target_vcpus_fast")
also added a check for multiple logical destinations before using
the fast-path. However, the same logic is already existed prior to
the commit. Therefore, remove redundant checking logic.

Fixes: 603ccef42ce9 ("KVM: x86: SVM: fix avic_kick_target_vcpus_fast")
Cc: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kvm/svm/avic.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 6919dee69f18..45ab49d1f0b8 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -378,8 +378,8 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 
 		if (apic_x2apic_mode(source)) {
 			/* 16 bit dest mask, 16 bit cluster id */
-			bitmap = dest & 0xFFFF0000;
-			cluster = (dest >> 16) << 4;
+			bitmap = dest & 0xffff;
+			cluster = (dest & 0xffff0000) >> 16;
 		} else if (kvm_lapic_get_reg(source, APIC_DFR) == APIC_DFR_FLAT) {
 			/* 8 bit dest mask*/
 			bitmap = dest;
@@ -387,7 +387,7 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 		} else {
 			/* 4 bit desk mask, 4 bit cluster id */
 			bitmap = dest & 0xF;
-			cluster = (dest >> 4) << 2;
+			cluster = (dest & 0xf0) >> 4;
 		}
 
 		if (unlikely(!bitmap))
@@ -420,18 +420,7 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 			 * For x2APIC logical mode, cannot leverage the index.
 			 * 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;
-
-			l1_physical_id = (cluster << 4) + apic;
+			l1_physical_id = (cluster << 4) + (ffs(bitmap) - 1);
 		}
 	}
 
-- 
2.34.1