[PULL 15/19] kvm: Persistent per kvmslot dirty bitmap

Juan Quintela
2019-07-11T10:45:06Z

From: Peter Xu <peterx@redhat.com>

When synchronizing dirty bitmap from kernel KVM we do it in a
per-kvmslot fashion and we allocate the userspace bitmap for each of
the ioctl. This patch instead make the bitmap cache be persistent
then we don't need to g_malloc0() every time.

More importantly, the cached per-kvmslot dirty bitmap will be further
used when we want to add support for the KVM_CLEAR_DIRTY_LOG and this
cached bitmap will be used to guarantee we won't clear any unknown
dirty bits otherwise that can be a severe data loss issue for
migration code.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20190603065056.25211-9-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
accel/kvm/kvm-all.c | 10 +++++++---
include/sysemu/kvm_int.h | 2 ++
2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index a3df19da56..23ace52b9e 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -516,17 +516,19 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
*/
size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
/*HOST_LONG_BITS*/ 64) / 8;
- d.dirty_bitmap = g_malloc0(size);
+ if (!mem->dirty_bmap) {
+ /* Allocate on the first log_sync, once and for all */
+ mem->dirty_bmap = g_malloc0(size);
+ }

+ d.dirty_bitmap = mem->dirty_bmap;
d.slot = mem->slot | (kml->as_id << 16);
if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
DPRINTF("ioctl failed %d\n", errno);
- g_free(d.dirty_bitmap);
return -1;
}

kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
- g_free(d.dirty_bitmap);
}

return 0;
@@ -801,6 +803,8 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
}

/* unregister the slot */
+ g_free(mem->dirty_bmap);
+ mem->dirty_bmap = NULL;
mem->memory_size = 0;
mem->flags = 0;
err = kvm_set_user_memory_region(kml, mem, false);
diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index f838412491..687a2ee423 100644
--- a/include/sysemu/kvm_int.h
+++ b/include/sysemu/kvm_int.h
@@ -21,6 +21,8 @@ typedef struct KVMSlot
int slot;
int flags;
int old_flags;
+ /* Dirty bitmap cache for the slot */
+ unsigned long *dirty_bmap;
} KVMSlot;

typedef struct KVMMemoryListener {
--
2.21.0