linux-kernel - [PATCH 7/8] KVM: VMX: Use arch_xchg() when processing PIR to avoid instrumentation

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Message-ID: <20250315030630.2371712-8-seanjc@google.com>
Date: Fri, 14 Mar 2025 20:06:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	Jacob Pan <jacob.jun.pan@...ux.intel.com>, Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 7/8] KVM: VMX: Use arch_xchg() when processing PIR to avoid instrumentation

Use arch_xchg() when moving IRQs from the PIR to the vIRR, purely to avoid
instrumentation so that KVM is compatible with the needs of posted MSI.
This will allow extracting the core PIR logic to common code and sharing
it between KVM and posted MSI handling.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/lapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index d7e36faffc72..b65e0f7223fe 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -680,7 +680,7 @@ bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr)
 		if (!pir_vals[i])
 			continue;
 
-		pir_vals[i] = xchg(&pir[i], 0);
+		pir_vals[i] = arch_xchg(&pir[i], 0);
 	}
 
 	for (i = vec = 0; i <= 7; i++, vec += 32) {
-- 
2.49.0.rc1.451.g8f38331e32-goog