linux-kernel - [PATCH] svm/avic: Allow avic_vcpu_load logic to support host APIC ID 255

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Message-ID: <1556890631-9561-1-git-send-email-suravee.suthikulpanit@amd.com>
Date:   Fri, 3 May 2019 13:37:27 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Subject: [PATCH] svm/avic: Allow avic_vcpu_load logic to support host APIC ID
 255

Current logic does not allow VCPU to be loaded onto CPU with
APIC ID 255. This should be allowed since the host physical APIC ID
field in the AVIC Physical APIC table entry is an 8-bit value,
and APIC ID 255 is valid in system with x2APIC enabled.

Instead, do not allow VCPU load if the host APIC ID cannot be
represented by an 8-bit value.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kvm/svm.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 294448e..122788f 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2071,7 +2071,11 @@ static void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (!kvm_vcpu_apicv_active(vcpu))
 		return;
 
-	if (WARN_ON(h_physical_id >= AVIC_MAX_PHYSICAL_ID_COUNT))
+	/*
+	 * Since the host physical APIC id is 8 bits,
+	 * we can support host APIC ID upto 255.
+	 */
+	if (WARN_ON(h_physical_id > AVIC_MAX_PHYSICAL_ID_COUNT))
 		return;
 
 	entry = READ_ONCE(*(svm->avic_physical_id_cache));
-- 
1.8.3.1