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 46efbe7..a8d8db8 100644 (file)
--- 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;
 }