Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com;
From:   Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
To:     <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>
CC:     <pbonzini@redhat.com>, <mlevitsk@redhat.com>, <seanjc@google.com>,
        <joro@8bytes.org>, <jon.grimm@amd.com>, <wei.huang2@amd.com>,
        <terry.bowman@amd.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: [PATCH v2 12/12] kvm/x86: Remove APICV activate mode inconsistency check
Date:   Tue, 12 Apr 2022 06:58:22 -0500
Message-ID: <20220412115822.14351-13-suravee.suthikulpanit@amd.com>
In-Reply-To: <20220412115822.14351-1-suravee.suthikulpanit@amd.com>
References: <20220412115822.14351-1-suravee.suthikulpanit@amd.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Apr 2022 11:59:16.8377
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: f05941a1-65ab-4aeb-c39a-08da1c7bdeb2
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT010.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4437
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE
	autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

When launching a VM with x2APIC and specify more than 255 vCPUs,
the guest kernel can disable x2APIC (e.g. specify nox2apic kernel option).
The VM fallbacks to xAPIC mode, and disable the vCPU ID 255.

In this case, APICV should be disabled for the vCPU ID 255.
Therefore, the APICV mode consisency check is no longer valid.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 arch/x86/kvm/x86.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0c0ca599a353..d0fac57e9996 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9765,6 +9765,11 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 	down_read(&vcpu->kvm->arch.apicv_update_lock);
 
 	activate = kvm_apicv_activated(vcpu->kvm);
+
+	/* Do not activate AVIC when APIC is disabled */
+	if (kvm_get_apic_mode(vcpu) == LAPIC_MODE_DISABLED)
+		activate = false;
+
 	if (vcpu->arch.apicv_active == activate)
 		goto out;
 
@@ -10159,14 +10164,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	guest_timing_enter_irqoff();
 
 	for (;;) {
-		/*
-		 * Assert that vCPU vs. VM APICv state is consistent.  An APICv
-		 * update must kick and wait for all vCPUs before toggling the
-		 * per-VM state, and responsing vCPUs must wait for the update
-		 * to complete before servicing KVM_REQ_APICV_UPDATE.
-		 */
-		WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
-
 		exit_fastpath = static_call(kvm_x86_vcpu_run)(vcpu);
 		if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
 			break;
-- 
2.25.1