linux-kernel - [PATCH 1/2] x86/apic: Export x2apic_mode for use by KVM in "warm" path

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Message-Id: <20210115220354.434807-2-seanjc@google.com>
Date:   Fri, 15 Jan 2021 14:03:53 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     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>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, luferry <luferry@....com>
Subject: [PATCH 1/2] x86/apic: Export x2apic_mode for use by KVM in "warm" path

Export x2apic_mode so that KVM can query whether x2APIC is active
without having to incur the RDMSR in x2apic_enabled().  When Posted
Interrupts are in use for a guest with an assigned device, KVM ends up
checking for x2APIC at least once every time a vCPU halts.  KVM could
obviously snapshot x2apic_enabled() to avoid the RDMSR, but that's
rather silly given that x2apic_mode holds the exact info needed by KVM.

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

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 6bd20c0de8bc..dea2b44966ca 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1743,6 +1743,7 @@ void apic_ap_setup(void)
 
 #ifdef CONFIG_X86_X2APIC
 int x2apic_mode;
+EXPORT_SYMBOL_GPL(x2apic_mode);
 
 enum {
 	X2APIC_OFF,
-- 
2.30.0.284.gd98b1dd5eaa7-goog