Re: [PATCH 5/6] vhost: mark dirty pages during map uninit
On Tue, Jul 23, 2019 at 09:19:33PM +0800, Jason Wang wrote:
>
> 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
> > > Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual
> > > address")
> > > Signed-off-by: Jason Wang
> > > ---
> > > 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.
>
> Thanks
>
OK. So the trick is that page_mkclean invokes mmu notifiers.
--
MST
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Re: [PATCH 5/6] vhost: mark dirty pages during map uninit
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
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang
---
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.
Thanks
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Re: [PATCH 5/6] vhost: mark dirty pages during map uninit
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
> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual
> address")
> Signed-off-by: Jason Wang
> ---
> 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.
> --
> 2.18.1
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