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From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	luferry <luferry@163.com>
Subject: [PATCH 1/2] x86/apic: Export x2apic_mode for use by KVM in "warm" path
Date: Fri, 15 Jan 2021 14:03:53 -0800	[thread overview]
Message-ID: <20210115220354.434807-2-seanjc@google.com> (raw)
In-Reply-To: <20210115220354.434807-1-seanjc@google.com>

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@google.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


  reply	other threads:[~2021-01-15 22:05 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-15 22:03 [PATCH 0/2] KVM: VMX: Avoid RDMSRs in PI x2APIC checks Sean Christopherson
2021-01-15 22:03 ` Sean Christopherson [this message]
2021-01-15 22:03 ` [PATCH 2/2] KVM: VMX: Use x2apic_mode to avoid RDMSR when querying PI state Sean Christopherson
2021-01-18 18:24 ` [PATCH 0/2] KVM: VMX: Avoid RDMSRs in PI x2APIC checks Paolo Bonzini

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