linux-kernel - [PATCH v2 27/43] KVM: VMX: Move Posted Interrupt ndst computation out of write loop

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Date:   Fri,  8 Oct 2021 19:12:20 -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 27/43] KVM: VMX: Move Posted Interrupt ndst computation out
 of write loop

Hoist the CPU => APIC ID conversion for the Posted Interrupt descriptor
out of the loop to write the descriptor, preemption is disabled so the
CPU won't change, and if the APIC ID changes KVM has bigger problems.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/posted_intr.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index fea343dcc011..2b2206339174 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -51,17 +51,15 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 		goto after_clear_sn;
 	}
 
-	/* The full case.  */
+	/* The full case.  Set the new destination and clear SN. */
+	dest = cpu_physical_id(cpu);
+	if (!x2apic_mode)
+		dest = (dest << 8) & 0xFF00;
+
 	do {
 		old.control = new.control = READ_ONCE(pi_desc->control);
 
-		dest = cpu_physical_id(cpu);
-
-		if (x2apic_mode)
-			new.ndst = dest;
-		else
-			new.ndst = (dest << 8) & 0xFF00;
-
+		new.ndst = dest;
 		new.sn = 0;
 	} while (cmpxchg64(&pi_desc->control, old.control,
 			   new.control) != old.control);
@@ -103,15 +101,14 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 	WARN(pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR,
 	     "Wakeup handler not enabled while the vCPU was blocking");
 
+	dest = cpu_physical_id(vcpu->cpu);
+	if (!x2apic_mode)
+		dest = (dest << 8) & 0xFF00;
+
 	do {
 		old.control = new.control = READ_ONCE(pi_desc->control);
 
-		dest = cpu_physical_id(vcpu->cpu);
-
-		if (x2apic_mode)
-			new.ndst = dest;
-		else
-			new.ndst = (dest << 8) & 0xFF00;
+		new.ndst = dest;
 
 		/* set 'NV' to 'notification vector' */
 		new.nv = POSTED_INTR_VECTOR;
-- 
2.33.0.882.g93a45727a2-goog