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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Chao Gao <chao.gao@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Sasha Levin <sashal@kernel.org>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, kvm@vger.kernel.org
Subject: [PATCH MANUALSEL 5.15 5/7] KVM: x86: Do not change ICR on write to APIC_SELF_IPI
Date:   Wed, 27 Apr 2022 11:54:25 -0400
Message-Id: <20220427155431.19458-5-sashal@kernel.org>
In-Reply-To: <20220427155431.19458-1-sashal@kernel.org>
References: <20220427155431.19458-1-sashal@kernel.org>
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From: Paolo Bonzini <pbonzini@redhat.com>

[ Upstream commit d22a81b304a27fca6124174a8e842e826c193466 ]

Emulating writes to SELF_IPI with a write to ICR has an unwanted side effect:
the value of ICR in vAPIC page gets changed.  The lists SELF_IPI as write-only,
with no associated MMIO offset, so any write should have no visible side
effect in the vAPIC page.

Reported-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/lapic.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4d92fb4fdf69..83d1743a1dd0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2125,10 +2125,9 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 		break;
 
 	case APIC_SELF_IPI:
-		if (apic_x2apic_mode(apic)) {
-			kvm_lapic_reg_write(apic, APIC_ICR,
-					    APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
-		} else
+		if (apic_x2apic_mode(apic))
+			kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
+		else
 			ret = 1;
 		break;
 	default:
-- 
2.35.1