On 2019/7/23 下午5:17, Michael S. Tsirkin wrote:
On Tue, Jul 23, 2019 at 03:57:17AM -0400, Jason Wang wrote:We don't mark dirty pages if the map was teared down outside MMU notifier. This will lead untracked dirty pages. Fixing by marking dirty pages during map uninit. Reported-by: Michael S. Tsirkin<mst@xxxxxxxxxx> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address") Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx> --- drivers/vhost/vhost.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 89c9f08b5146..5b8821d00fe4 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -306,6 +306,18 @@ static void vhost_map_unprefetch(struct vhost_map *map) kfree(map); }+static void vhost_set_map_dirty(struct vhost_virtqueue *vq,+ struct vhost_map *map, int index) +{ + struct vhost_uaddr *uaddr = &vq->uaddrs[index]; + int i; + + if (uaddr->write) { + for (i = 0; i < map->npages; i++) + set_page_dirty(map->pages[i]); + } +} + static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq) { struct vhost_map *map[VHOST_NUM_ADDRS]; @@ -315,8 +327,10 @@ static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq) for (i = 0; i < VHOST_NUM_ADDRS; i++) { map[i] = rcu_dereference_protected(vq->maps[i], lockdep_is_held(&vq->mmu_lock)); - if (map[i]) + if (map[i]) { + vhost_set_map_dirty(vq, map[i], i); rcu_assign_pointer(vq->maps[i], NULL); + } } spin_unlock(&vq->mmu_lock);@@ -354,7 +368,6 @@ static void vhost_invalidate_vq_start(struct vhost_virtqueue *vq,{ struct vhost_uaddr *uaddr = &vq->uaddrs[index]; struct vhost_map *map; - int i;if (!vhost_map_range_overlap(uaddr, start, end))return; @@ -365,10 +378,7 @@ static void vhost_invalidate_vq_start(struct vhost_virtqueue *vq, map = rcu_dereference_protected(vq->maps[index], lockdep_is_held(&vq->mmu_lock)); if (map) { - if (uaddr->write) { - for (i = 0; i < map->npages; i++) - set_page_dirty(map->pages[i]); - } + vhost_set_map_dirty(vq, map, index); rcu_assign_pointer(vq->maps[index], NULL); } spin_unlock(&vq->mmu_lock);OK and the reason it's safe is because the invalidate counter got incremented so we know page will not get mapped again. But we*do* need to wait for page not to be mapped. And if that means waiting for VQ processing to finish, then I worry that is a very log time.
I'm not sure I get you here. If we don't have such map, we will fall back to normal uaccess helper. And in the memory accessor, the rcu critical section is pretty small.
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