Both virtqueue_packed_get_avail_bytes() and
virtqueue_split_get_avail_bytes() access the region cache, but
their caller also does. Simplify by having virtqueue_get_avail_bytes
calling both with RCU lock held, and passing the caches as argument.
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
RFC because I'm not sure this is safe enough
---
hw/virtio/virtio.c | 29 ++++++++++++-----------------
1 file changed, 12 insertions(+), 17 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 3a1f6c520cb..8237693a567 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -984,28 +984,23 @@ static int virtqueue_split_read_next_desc(VirtIODevice *vdev, VRingDesc *desc,
return VIRTQUEUE_READ_DESC_MORE;
}
+/* Called within rcu_read_lock(). */
static void virtqueue_split_get_avail_bytes(VirtQueue *vq,
unsigned int *in_bytes, unsigned int *out_bytes,
- unsigned max_in_bytes, unsigned max_out_bytes)
+ unsigned max_in_bytes, unsigned max_out_bytes,
+ VRingMemoryRegionCaches *caches)
{
VirtIODevice *vdev = vq->vdev;
unsigned int max, idx;
unsigned int total_bufs, in_total, out_total;
- VRingMemoryRegionCaches *caches;
MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
int64_t len = 0;
int rc;
- RCU_READ_LOCK_GUARD();
-
idx = vq->last_avail_idx;
total_bufs = in_total = out_total = 0;
max = vq->vring.num;
- caches = vring_get_region_caches(vq);
- if (!caches) {
- goto err;
- }
while ((rc = virtqueue_num_heads(vq, idx)) > 0) {
MemoryRegionCache *desc_cache = &caches->desc;
@@ -1124,32 +1119,28 @@ static int virtqueue_packed_read_next_desc(VirtQueue *vq,
return VIRTQUEUE_READ_DESC_MORE;
}
+/* Called within rcu_read_lock(). */
static void virtqueue_packed_get_avail_bytes(VirtQueue *vq,
unsigned int *in_bytes,
unsigned int *out_bytes,
unsigned max_in_bytes,
- unsigned max_out_bytes)
+ unsigned max_out_bytes,
+ VRingMemoryRegionCaches *caches)
{
VirtIODevice *vdev = vq->vdev;
unsigned int max, idx;
unsigned int total_bufs, in_total, out_total;
MemoryRegionCache *desc_cache;
- VRingMemoryRegionCaches *caches;
MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
int64_t len = 0;
VRingPackedDesc desc;
bool wrap_counter;
- RCU_READ_LOCK_GUARD();
idx = vq->last_avail_idx;
wrap_counter = vq->last_avail_wrap_counter;
total_bufs = in_total = out_total = 0;
max = vq->vring.num;
- caches = vring_get_region_caches(vq);
- if (!caches) {
- goto err;
- }
for (;;) {
unsigned int num_bufs = total_bufs;
@@ -1250,6 +1241,8 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
uint16_t desc_size;
VRingMemoryRegionCaches *caches;
+ RCU_READ_LOCK_GUARD();
+
if (unlikely(!vq->vring.desc)) {
goto err;
}
@@ -1268,10 +1261,12 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
virtqueue_packed_get_avail_bytes(vq, in_bytes, out_bytes,
- max_in_bytes, max_out_bytes);
+ max_in_bytes, max_out_bytes,
+ caches);
} else {
virtqueue_split_get_avail_bytes(vq, in_bytes, out_bytes,
- max_in_bytes, max_out_bytes);
+ max_in_bytes, max_out_bytes,
+ caches);
}
return;
--
2.31.1
On Thu, Aug 26, 2021 at 07:26:58PM +0200, Philippe Mathieu-Daudé wrote:
>Both virtqueue_packed_get_avail_bytes() and
>virtqueue_split_get_avail_bytes() access the region cache, but
>their caller also does. Simplify by having virtqueue_get_avail_bytes
>calling both with RCU lock held, and passing the caches as argument.
>
>Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>---
>RFC because I'm not sure this is safe enough
It seems safe to me.
While reviewing I saw that vring_get_region_caches() has
/* Called within rcu_read_lock(). */ comment, but it seems to me that
we call that function in places where we haven't acquired it, which
shouldn't be a problem, but should we remove that comment?
Thanks,
Stefano
>---
> hw/virtio/virtio.c | 29 ++++++++++++-----------------
> 1 file changed, 12 insertions(+), 17 deletions(-)
>
>diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>index 3a1f6c520cb..8237693a567 100644
>--- a/hw/virtio/virtio.c
>+++ b/hw/virtio/virtio.c
>@@ -984,28 +984,23 @@ static int virtqueue_split_read_next_desc(VirtIODevice *vdev, VRingDesc *desc,
> return VIRTQUEUE_READ_DESC_MORE;
> }
>
>+/* Called within rcu_read_lock(). */
> static void virtqueue_split_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes, unsigned int *out_bytes,
>- unsigned max_in_bytes, unsigned max_out_bytes)
>+ unsigned max_in_bytes, unsigned max_out_bytes,
>+ VRingMemoryRegionCaches *caches)
> {
> VirtIODevice *vdev = vq->vdev;
> unsigned int max, idx;
> unsigned int total_bufs, in_total, out_total;
>- VRingMemoryRegionCaches *caches;
> MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
> int64_t len = 0;
> int rc;
>
>- RCU_READ_LOCK_GUARD();
>-
> idx = vq->last_avail_idx;
> total_bufs = in_total = out_total = 0;
>
> max = vq->vring.num;
>- caches = vring_get_region_caches(vq);
>- if (!caches) {
>- goto err;
>- }
>
> while ((rc = virtqueue_num_heads(vq, idx)) > 0) {
> MemoryRegionCache *desc_cache = &caches->desc;
>@@ -1124,32 +1119,28 @@ static int virtqueue_packed_read_next_desc(VirtQueue *vq,
> return VIRTQUEUE_READ_DESC_MORE;
> }
>
>+/* Called within rcu_read_lock(). */
> static void virtqueue_packed_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes,
> unsigned int *out_bytes,
> unsigned max_in_bytes,
>- unsigned max_out_bytes)
>+ unsigned max_out_bytes,
>+ VRingMemoryRegionCaches *caches)
> {
> VirtIODevice *vdev = vq->vdev;
> unsigned int max, idx;
> unsigned int total_bufs, in_total, out_total;
> MemoryRegionCache *desc_cache;
>- VRingMemoryRegionCaches *caches;
> MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
> int64_t len = 0;
> VRingPackedDesc desc;
> bool wrap_counter;
>
>- RCU_READ_LOCK_GUARD();
> idx = vq->last_avail_idx;
> wrap_counter = vq->last_avail_wrap_counter;
> total_bufs = in_total = out_total = 0;
>
> max = vq->vring.num;
>- caches = vring_get_region_caches(vq);
>- if (!caches) {
>- goto err;
>- }
>
> for (;;) {
> unsigned int num_bufs = total_bufs;
>@@ -1250,6 +1241,8 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
> uint16_t desc_size;
> VRingMemoryRegionCaches *caches;
>
>+ RCU_READ_LOCK_GUARD();
>+
> if (unlikely(!vq->vring.desc)) {
> goto err;
> }
>@@ -1268,10 +1261,12 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
>
> if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> virtqueue_packed_get_avail_bytes(vq, in_bytes, out_bytes,
>- max_in_bytes, max_out_bytes);
>+ max_in_bytes, max_out_bytes,
>+ caches);
> } else {
> virtqueue_split_get_avail_bytes(vq, in_bytes, out_bytes,
>- max_in_bytes, max_out_bytes);
>+ max_in_bytes, max_out_bytes,
>+ caches);
> }
>
> return;
>--
>2.31.1
>
>
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