linux-kernel - [PATCH v2 21/43] KVM: VMX: Clean up PI pre/post-block WARNs

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Message-Id: <20211009021236.4122790-22-seanjc@google.com>
Date:   Fri,  8 Oct 2021 19:12:14 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: [PATCH v2 21/43] KVM: VMX: Clean up PI pre/post-block WARNs

Move the WARN sanity checks out of the PI descriptor update loop so as
not to spam the kernel log if the condition is violated and the update
takes multiple attempts due to another writer.  This also eliminates a
few extra uops from the retry path.

Technically not checking every attempt could mean KVM will now fail to
WARN in a scenario that would have failed before, but any such failure
would be inherently racy as some other agent (CPU or device) would have
to concurrent modify the PI descriptor.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/posted_intr.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 351666c41bbc..67cbe6ab8f66 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -100,10 +100,11 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 	struct pi_desc old, new;
 	unsigned int dest;
 
+	WARN(pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR,
+	     "Wakeup handler not enabled while the vCPU was blocking");
+
 	do {
 		old.control = new.control = pi_desc->control;
-		WARN(old.nv != POSTED_INTR_WAKEUP_VECTOR,
-		     "Wakeup handler not enabled while the VCPU is blocked\n");
 
 		dest = cpu_physical_id(vcpu->cpu);
 
@@ -161,13 +162,12 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
 		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
 	}
 
+	WARN(pi_desc->sn == 1,
+	     "Posted Interrupt Suppress Notification set before blocking");
+
 	do {
 		old.control = new.control = pi_desc->control;
 
-		WARN((pi_desc->sn == 1),
-		     "Warning: SN field of posted-interrupts "
-		     "is set before blocking\n");
-
 		/*
 		 * Since vCPU can be preempted during this process,
 		 * vcpu->cpu could be different with pre_pcpu, we
-- 
2.33.0.882.g93a45727a2-goog