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From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Li RongQing <lirongqing@baidu.com>
Subject: [PATCH v2 10/23] KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch
Date: Sat,  3 Sep 2022 00:22:41 +0000	[thread overview]
Message-ID: <20220903002254.2411750-11-seanjc@google.com> (raw)
In-Reply-To: <20220903002254.2411750-1-seanjc@google.com>

Document that AVIC is inhibited if any vCPU's APIC ID diverges from its
vCPU ID, i.e. that there's no need to check for a destination match in
the AVIC kick fast path.

Opportunistically tweak comments to remove "guest bug", as that suggests
KVM is punting on error handling, which is not the case.  Targeting a
non-existent vCPU or no vCPUs _may_ be a guest software bug, but whether
or not it's a guest bug is irrelevant.  Such behavior is architecturally
legal and thus needs to faithfully emulated by KVM (and it is).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/svm/avic.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 8259a64c99d6..b4b5f1422db7 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -395,8 +395,8 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 			cluster = (dest >> 4) << 2;
 		}
 
+		/* Nothing to do if there are no destinations in the cluster. */
 		if (unlikely(!bitmap))
-			/* guest bug: nobody to send the logical interrupt to */
 			return 0;
 
 		if (!is_power_of_2(bitmap))
@@ -424,7 +424,7 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 			if (WARN_ON_ONCE(index != logid_index))
 				return -EINVAL;
 
-			/* guest bug: non existing/reserved logical destination */
+			/* Nothing to do if the logical destination is invalid. */
 			if (unlikely(!(logid_entry & AVIC_LOGICAL_ID_ENTRY_VALID_MASK)))
 				return 0;
 
@@ -433,9 +433,13 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
 		}
 	}
 
+	/*
+	 * KVM inhibits AVIC if any vCPU ID diverges from the vCPUs APIC ID,
+	 * i.e. APIC ID == vCPU ID.  Once again, nothing to do if the target
+	 * vCPU doesn't exist.
+	 */
 	target_vcpu = kvm_get_vcpu_by_id(kvm, l1_physical_id);
 	if (unlikely(!target_vcpu))
-		/* guest bug: non existing vCPU is a target of this IPI*/
 		return 0;
 
 	target_vcpu->arch.apic->irr_pending = true;
-- 
2.37.2.789.g6183377224-goog


  parent reply	other threads:[~2022-09-03  0:23 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-03  0:22 [PATCH v2 00/23] KVM: x86: AVIC and local APIC fixes+cleanups Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 01/23] KVM: x86: Purge "highest ISR" cache when updating APICv state Sean Christopherson
2022-09-05 21:58   ` Paolo Bonzini
2022-09-03  0:22 ` [PATCH v2 02/23] KVM: SVM: Flush the "current" TLB when activating AVIC Sean Christopherson
2022-09-05 21:58   ` Paolo Bonzini
2022-09-03  0:22 ` [PATCH v2 03/23] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target Sean Christopherson
2022-09-05 21:59   ` Paolo Bonzini
2022-09-03  0:22 ` [PATCH v2 04/23] KVM: x86: Inhibit AVIC SPTEs if any vCPU enables x2APIC Sean Christopherson
2022-09-05 22:02   ` Paolo Bonzini
2022-09-13 19:52   ` Suthikulpanit, Suravee
2022-09-14  7:39     ` Sean Christopherson
2022-09-14 17:41       ` Suthikulpanit, Suravee
2022-09-16 17:47         ` Sean Christopherson
2022-09-16 19:10     ` Sean Christopherson
2022-09-20 13:07   ` Maxim Levitsky
2022-09-20 15:46     ` Sean Christopherson
2022-09-20 16:50       ` Sean Christopherson
2022-09-23 10:18         ` Maxim Levitsky
2022-09-23 10:19       ` Maxim Levitsky
2022-09-03  0:22 ` [PATCH v2 05/23] KVM: SVM: Don't put/load AVIC when setting virtual APIC mode Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 06/23] KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 07/23] KVM: SVM: Compute dest based on sender's x2APIC status for AVIC kick Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 08/23] KVM: SVM: Fix x2APIC Logical ID calculation for avic_kick_target_vcpus_fast Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 09/23] Revert "KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible" Sean Christopherson
2022-09-03  0:22 ` Sean Christopherson [this message]
2022-09-03  0:22 ` [PATCH v2 11/23] KVM: SVM: Add helper to perform final AVIC "kick" of single vCPU Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 12/23] KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 13/23] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode Sean Christopherson
2022-09-13 23:32   ` Suthikulpanit, Suravee
2022-09-14  7:42     ` Sean Christopherson
2022-09-15  2:11       ` Suthikulpanit, Suravee
2022-09-16 18:52         ` Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 14/23] KVM: x86: Honor architectural behavior for aliased 8-bit APIC IDs Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 15/23] KVM: x86: Explicitly skip adding vCPU to optimized logical map if LDR==0 Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 16/23] KVM: x86: Explicitly track all possibilities for APIC map's logical modes Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 17/23] KVM: SVM: Inhibit AVIC if vCPUs are aliased in logical mode Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 18/23] KVM: SVM: Always update local APIC on writes to logical dest register Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 19/23] KVM: SVM: Update svm->ldr_reg cache even if LDR is "bad" Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 20/23] KVM: SVM: Require logical ID to be power-of-2 for AVIC entry Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 21/23] KVM: SVM: Handle multiple logical targets in AVIC kick fastpath Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 22/23] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps Sean Christopherson
2022-09-03  0:22 ` [PATCH v2 23/23] Revert "KVM: SVM: Do not throw warning when calling avic_vcpu_load on a running vcpu" Sean Christopherson

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