linux-kernel - [PATCH v2] svm/avic: Allow avic_vcpu_load logic to support host APIC ID 255

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Date:   Tue, 14 May 2019 15:49:52 +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>,
        "graf@...zon.com" <graf@...zon.com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Subject: [PATCH v2] 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.

Also, use the more appropriate AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK
instead of AVIC_MAX_PHYSICAL_ID_COUNT. 

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---

Change in V2:
  * Use AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK instead of
    AVIC_MAX_PHYSICAL_ID_COUNT. 

 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 687767f..345fe9e 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_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK))
 		return;
 
 	entry = READ_ONCE(*(svm->avic_physical_id_cache));
-- 
1.8.3.1