Messages in this thread | | | From | 黄杰 <> | Date | Thu, 16 Jun 2022 15:39:27 +0800 | Subject | Re: [External] Re: [PATCH v2] virtio_ring : keep used_wrap_counter in vq->last_used_idx |
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Michael S. Tsirkin <mst@redhat.com> 于2022年6月16日周四 14:42写道: > > On Thu, Jun 16, 2022 at 02:07:19AM -0400, Michael S. Tsirkin wrote: > > On Thu, Jun 16, 2022 at 01:12:21PM +0800, Albert Huang wrote: > > > From: "huangjie.albert" <huangjie.albert@bytedance.com> > > > > > > the used_wrap_counter and the vq->last_used_idx may get > > > out of sync if they are separate assignment,and interrupt > > > might use an incorrect value to check for the used index. > > > > > > for example:OOB access > > > ksoftirqd may consume the packet and it will call: > > > virtnet_poll > > > -->virtnet_receive > > > -->virtqueue_get_buf_ctx > > > -->virtqueue_get_buf_ctx_packed > > > and in virtqueue_get_buf_ctx_packed: > > > > > > vq->last_used_idx += vq->packed.desc_state[id].num; > > > if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) { > > > vq->last_used_idx -= vq->packed.vring.num; > > > vq->packed.used_wrap_counter ^= 1; > > > } > > > > > > if at the same time, there comes a vring interrupt,in vring_interrupt: > > > we will call: > > > vring_interrupt > > > -->more_used > > > -->more_used_packed > > > -->is_used_desc_packed > > > in is_used_desc_packed, the last_used_idx maybe >= vq->packed.vring.num. > > > so this could case a memory out of bounds bug. > > > > > > this patch is to keep the used_wrap_counter in vq->last_used_idx > > > so we can get the correct value to check for used index in interrupt. > > > > > > v1->v2: > > > - reuse the VRING_PACKED_EVENT_F_WRAP_CTR > > > - Remove parameter judgment in is_used_desc_packed, > > > because it can't be illegal > > > > > > Signed-off-by: huangjie.albert <huangjie.albert@bytedance.com> > > > > > > This looks good, just a small suggestion below: > > > > > --- > > > drivers/virtio/virtio_ring.c | 57 ++++++++++++++++++++---------------- > > > 1 file changed, 31 insertions(+), 26 deletions(-) > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > index 13a7348cedff..b22d97c9a755 100644 > > > --- a/drivers/virtio/virtio_ring.c > > > +++ b/drivers/virtio/virtio_ring.c > > > @@ -111,7 +111,12 @@ struct vring_virtqueue { > > > /* Number we've added since last sync. */ > > > unsigned int num_added; > > > > > > - /* Last used index we've seen. */ > > > + /* Last used index we've seen. > > > + * for split ring, it just contains last used index > > > + * for packed ring, it not only contains last used index, but also > > > + * used_wrap_counter, the VRING_PACKED_EVENT_F_WRAP_CTR is > > > + * the bit shift in last_used_idx > > > + */ > > > u16 last_used_idx; > > > > > > /* Hint for event idx: already triggered no need to disable. */ > > > @@ -154,9 +159,6 @@ struct vring_virtqueue { > > > /* Driver ring wrap counter. */ > > > bool avail_wrap_counter; > > > > > > - /* Device ring wrap counter. */ > > > - bool used_wrap_counter; > > > - > > > /* Avail used flags. */ > > > u16 avail_used_flags; > > > > > > @@ -1406,8 +1408,12 @@ static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > > > > > > static inline bool more_used_packed(const struct vring_virtqueue *vq) > > > { > > > - return is_used_desc_packed(vq, vq->last_used_idx, > > > - vq->packed.used_wrap_counter); > > > + u16 last_used; > > > + bool used_wrap_counter; > > > + > > > + last_used = vq->last_used_idx & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR); > > > > This only works if last_used_idx is 16 bit and > > VRING_PACKED_EVENT_F_WRAP_CTR is 15. > > > > I think you want > > /* all bits below VRING_PACKED_EVENT_F_WRAP_CTR */ > > vq->last_used_idx & ~(-(1 << VRING_PACKED_EVENT_F_WRAP_CTR)); > > > > > > > + used_wrap_counter = !!((vq->last_used_idx) >> VRING_PACKED_EVENT_F_WRAP_CTR); > > > > > > A bit more efficient and clear: > > > > !!(q->last_used_idx & (1 << VRING_PACKED_EVENT_F_WRAP_CTR)) > > > > > > > > Also this logic is repeated in multiple places. Let's add a couple of inline > > functions: > > > > static inline bool packed_used_wrap_counter(vq) > > > > static inline u16 packed_last_used(vq) > > Or better: > > packed_used_wrap_counter(u16 last_used_idx) > packed_last_used(u16 last_used_idx) >
This one does look better, Jason what is your take?
thanks.
> > then use these everywhere. > > > > > > > + return is_used_desc_packed(vq, last_used, used_wrap_counter); > > > } > > > > > > static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > > @@ -1416,6 +1422,7 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > u16 last_used, id; > > > + bool used_wrap_counter; > > > void *ret; > > > > > > START_USE(vq); > > > @@ -1434,7 +1441,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > > /* Only get used elements after they have been exposed by host. */ > > > virtio_rmb(vq->weak_barriers); > > > > > > - last_used = vq->last_used_idx; > > > + used_wrap_counter = !!((vq->last_used_idx >> VRING_PACKED_EVENT_F_WRAP_CTR)); > > > + last_used = (vq->last_used_idx) & (~(1 << VRING_PACKED_EVENT_F_WRAP_CTR)); > > > id = le16_to_cpu(vq->packed.vring.desc[last_used].id); > > > *len = le32_to_cpu(vq->packed.vring.desc[last_used].len); > > > > > > @@ -1451,12 +1459,15 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > > ret = vq->packed.desc_state[id].data; > > > detach_buf_packed(vq, id, ctx); > > > > > > - vq->last_used_idx += vq->packed.desc_state[id].num; > > > - if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) { > > > - vq->last_used_idx -= vq->packed.vring.num; > > > - vq->packed.used_wrap_counter ^= 1; > > > + last_used += vq->packed.desc_state[id].num; > > > + if (unlikely(last_used >= vq->packed.vring.num)) { > > > + last_used -= vq->packed.vring.num; > > > + used_wrap_counter ^= 1; > > > } > > > > > > + last_used = (last_used | (used_wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR)); > > > + vq->last_used_idx = last_used; > > > + > > > /* > > > * If we expect an interrupt for the next entry, tell host > > > * by writing event index and flush out the write before > > > @@ -1465,9 +1476,7 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > > if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC) > > > virtio_store_mb(vq->weak_barriers, > > > &vq->packed.vring.driver->off_wrap, > > > - cpu_to_le16(vq->last_used_idx | > > > - (vq->packed.used_wrap_counter << > > > - VRING_PACKED_EVENT_F_WRAP_CTR))); > > > + cpu_to_le16(vq->last_used_idx)); > > > > > > LAST_ADD_TIME_INVALID(vq); > > > > > > @@ -1499,9 +1508,7 @@ static unsigned int virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > > > > > if (vq->event) { > > > vq->packed.vring.driver->off_wrap = > > > - cpu_to_le16(vq->last_used_idx | > > > - (vq->packed.used_wrap_counter << > > > - VRING_PACKED_EVENT_F_WRAP_CTR)); > > > + cpu_to_le16(vq->last_used_idx); > > > /* > > > * We need to update event offset and event wrap > > > * counter first before updating event flags. > > > @@ -1518,8 +1525,7 @@ static unsigned int virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > > } > > > > > > END_USE(vq); > > > - return vq->last_used_idx | ((u16)vq->packed.used_wrap_counter << > > > - VRING_PACKED_EVENT_F_WRAP_CTR); > > > + return vq->last_used_idx; > > > } > > > > > > static bool virtqueue_poll_packed(struct virtqueue *_vq, u16 off_wrap) > > > @@ -1550,9 +1556,9 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > > > if (vq->event) { > > > /* TODO: tune this threshold */ > > > bufs = (vq->packed.vring.num - vq->vq.num_free) * 3 / 4; > > > - wrap_counter = vq->packed.used_wrap_counter; > > > + wrap_counter = !!(vq->last_used_idx >> VRING_PACKED_EVENT_F_WRAP_CTR); > > > > > > - used_idx = vq->last_used_idx + bufs; > > > + used_idx = (vq->last_used_idx & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR)) + bufs; > > > if (used_idx >= vq->packed.vring.num) { > > > used_idx -= vq->packed.vring.num; > > > wrap_counter ^= 1; > > > @@ -1582,9 +1588,9 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > > > */ > > > virtio_mb(vq->weak_barriers); > > > > > > - if (is_used_desc_packed(vq, > > > - vq->last_used_idx, > > > - vq->packed.used_wrap_counter)) { > > > + wrap_counter = !!(vq->last_used_idx >> VRING_PACKED_EVENT_F_WRAP_CTR); > > > + used_idx = (vq->last_used_idx & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR)); > > > + if (is_used_desc_packed(vq, used_idx, wrap_counter)) { > > > END_USE(vq); > > > return false; > > > } > > > @@ -1689,7 +1695,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > > > vq->notify = notify; > > > vq->weak_barriers = weak_barriers; > > > vq->broken = true; > > > - vq->last_used_idx = 0; > > > + vq->last_used_idx = 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR); > > > vq->event_triggered = false; > > > vq->num_added = 0; > > > vq->packed_ring = true; > > > @@ -1720,7 +1726,6 @@ static struct virtqueue *vring_create_virtqueue_packed( > > > > > > vq->packed.next_avail_idx = 0; > > > vq->packed.avail_wrap_counter = 1; > > > - vq->packed.used_wrap_counter = 1; > > > vq->packed.event_flags_shadow = 0; > > > vq->packed.avail_used_flags = 1 << VRING_PACKED_DESC_F_AVAIL; > > > > > > -- > > > 2.31.1 >
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