linux-kernel - [PATCH 03/58] KVM: Assume that writes smaller than 4 bytes are to non-pagetable pages

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Message-Id: <1182073479448-git-send-email-avi@qumranet.com>
Date:	Sun, 17 Jun 2007 12:43:44 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>
Subject: [PATCH 03/58] KVM: Assume that writes smaller than 4 bytes are to non-pagetable pages

This allows us to remove write protection earlier than otherwise.  Should
some mad OS choose to use byte writes to update pagetables, it will suffer
a performance hit, but still work correctly.

Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 drivers/kvm/mmu.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index e8e2281..2277b7c 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -1169,6 +1169,7 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes)
 			continue;
 		pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8;
 		misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
+		misaligned |= bytes < 4;
 		if (misaligned || flooded) {
 			/*
 			 * Misaligned accesses are too much trouble to fix
-- 
1.5.0.6

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