[Qemu-devel] [PATCH 7/7] Fake dirty loggin when it's not there

[Alexander Graf <agraf@suse.de>]

Some KVM platforms don't support dirty logging yet, like IA64 and PPC,
so in order to still have screen updates on those, we need to fake it.

This patch just tells the getter function for dirty bitmaps, that all
pages within a slot are dirty when the slot has dirty logging enabled.

That way we can implement dirty logging on those platforms sometime when
it drags down performance, but share the rest of the code with dirty
logging capable platforms.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 kvm-all.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index 60b76cf..72b7935 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -300,6 +300,7 @@ int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
     KVMDirtyLog d;
     KVMSlot *mem;
     int ret = 0;
+    int r;
 
     d.dirty_bitmap = NULL;
     while (start_addr < end_addr) {
@@ -308,6 +309,11 @@ int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
             break;
         }
 
+        /* We didn't activate dirty logging? Don't care then. */
+        if(!(mem->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
+            continue;
+        }
+
         size = ((mem->memory_size >> TARGET_PAGE_BITS) + 7) / 8;
         if (!d.dirty_bitmap) {
             d.dirty_bitmap = qemu_malloc(size);
@@ -319,7 +325,8 @@ int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
 
         d.slot = mem->slot;
 
-        if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
+        r = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
+        if (r == -EINVAL) {
             dprintf("ioctl failed %d\n", errno);
             ret = -1;
             break;
@@ -335,6 +342,10 @@ int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
 
             if ((bitmap[word] >> bit) & 1) {
                 cpu_physical_memory_set_dirty(addr);
+            } else if (r < 0) {
+                /* When our KVM implementation doesn't know about dirty logging
+                 * we can just assume it's always dirty and be fine. */
+                cpu_physical_memory_set_dirty(addr);
             }
         }
         start_addr = phys_addr;
-- 
1.6.0.2