linux-kernel - [PATCHv6 1/8] kvm: document lapic regs field

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Date:	Sun, 3 Jun 2012 10:27:53 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	x86@...nel.org, kvm@...r.kernel.org
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, gleb@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCHv6 1/8] kvm: document lapic regs field

The logic in find_highest_vector looks
strange until you realize the reason for the
weird memory layout, which is because this is
what the CPU microcode expects.

Add a comment so this stops tripping people up.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 arch/x86/kvm/lapic.h |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 6f4ce25..d29da25 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -13,6 +13,11 @@ struct kvm_lapic {
 	u32 divide_count;
 	struct kvm_vcpu *vcpu;
 	bool irr_pending;
+	/**
+	 * APIC register page.  The layout matches the register layout seen by
+	 * the guest 1:1, because it is accessed by the vmx microcode.
+	 * Note: Only one register, the TPR, is used by the microcode.
+	 */
 	void *regs;
 	gpa_t vapic_addr;
 	struct page *vapic_page;
-- 
MST

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