KVM: Avoid useless memory write when possible

When writing to normal memory and the memory area is unchanged the write can be safely skipped, avoiding the costly kvm_mmu_pte_write. Signed-Off-By: Luca Tettamanti <[email protected]> Signed-off-by: Avi Kivity <[email protected]>
vjousse · Jul 16, 2007 · a3c870b · a3c870b
1 parent 02c03a3
commit a3c870b
Showing 1 changed file with 4 additions and 2 deletions.
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
@@ -1170,8 +1170,10 @@ 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);
-	kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
-	memcpy(virt + offset_in_page(gpa), val, bytes);
+	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);
+	}
 	kunmap_atomic(virt, KM_USER0);
 	return 1;
 }