From: Avi Kivity <avi@qumranet.com>
Date: Mon, 23 Jul 2007 15:33:14 +0000 (+0300)
Subject: Revert "KVM: Avoid useless memory write when possible"
X-Git-Tag: v2.6.23-rc2~286^2~2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7cfa4b0a43286b1da3afa4f5f99d52e65a8f30fc;p=linux-2.6

Revert "KVM: Avoid useless memory write when possible"

This reverts commit a3c870bdce4d34332ebdba7eb9969592c4c6b243.  While it
does save useless updates, it (probably) defeats the fork detector, causing
a massive performance loss.

Signed-off-by: Avi Kivity <avi@qumranet.com>
---

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 46efbe7080..a8d8db8e3c 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1070,10 +1070,8 @@ static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
 		return 0;
 	mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT);
 	virt = kmap_atomic(page, KM_USER0);
-	if (memcmp(virt + offset_in_page(gpa), val, bytes)) {
-		kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
-		memcpy(virt + offset_in_page(gpa), val, bytes);
-	}
+	kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
+	memcpy(virt + offset_in_page(gpa), val, bytes);
 	kunmap_atomic(virt, KM_USER0);
 	return 1;
 }