Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

2021-03-22 Thread Jason Wang 



在 2021/3/22 下午4:17, Michael S. Tsirkin 写道:

On Mon, Mar 22, 2021 at 11:22:15AM +0800, Jason Wang wrote:

在 2021/3/18 下午9:52, Connor Kuehl 写道:

  From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
of the virtio spec:

"A driver MUST NOT create a descriptor chain longer than the Queue
Size of the device."

This text suggests that the warning should trigger even if
indirect descriptors are in use.


So I think at least the commit log needs some tweak.

For split virtqueue. We had:

2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table

Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total;
this implies that loops in the descriptor chain are forbidden!

2.6.5.3.1 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than the Queue Size of
the device.

If I understand the spec correctly, the check is only needed for a single
indirect descriptor table?

For packed virtqueue. We had:

2.7.17 Driver Requirements: Scatter-Gather Support

A driver MUST NOT create a descriptor list longer than allowed by the
device.

A driver MUST NOT create a descriptor list longer than the Queue Size.

2.7.19 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than allowed by the
device.

So it looks to me the packed part is fine.

Note that if I understand the spec correctly 2.7.17 implies 2.7.19.

Thanks

It would be quite strange for packed and split to differ here:
so for packed would you say there's no limit on # of descriptors at all?

I am guessing I just forgot to move this part from
the format specific to the common part of the spec.

This needs discussion in the TC mailing list - want to start a thread
there?



Will do.

Thanks







Reported-by: Stefan Hajnoczi 
Signed-off-by: Connor Kuehl 
---
   drivers/virtio/virtio_ring.c | 7 ---
   1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..1bc290f9ba13 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue 
*_vq,
head = vq->free_head;
+   WARN_ON_ONCE(total_sg > vq->split.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
desc = alloc_indirect_split(_vq, total_sg, gfp);
else {
desc = NULL;
-   WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
}
if (desc) {
@@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
BUG_ON(total_sg == 0);
+   WARN_ON_ONCE(total_sg > vq->packed.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
return virtqueue_add_indirect_packed(vq, sgs, total_sg,
out_sgs, in_sgs, data, gfp);
@@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
head = vq->packed.next_avail_idx;
avail_used_flags = vq->packed.avail_used_flags;
-   WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
-
desc = vq->packed.vring.desc;
i = head;
descs_used = total_sg;

Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

2021-03-22 Thread Michael S. Tsirkin 
On Mon, Mar 22, 2021 at 11:22:15AM +0800, Jason Wang wrote:
> 
> 在 2021/3/18 下午9:52, Connor Kuehl 写道:
> >  From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
> > of the virtio spec:
> > 
> >"A driver MUST NOT create a descriptor chain longer than the Queue
> >Size of the device."
> > 
> > This text suggests that the warning should trigger even if
> > indirect descriptors are in use.
> 
> 
> So I think at least the commit log needs some tweak.
> 
> For split virtqueue. We had:
> 
> 2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table
> 
> Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total;
> this implies that loops in the descriptor chain are forbidden!
> 
> 2.6.5.3.1 Driver Requirements: Indirect Descriptors
> 
> A driver MUST NOT create a descriptor chain longer than the Queue Size of
> the device.
> 
> If I understand the spec correctly, the check is only needed for a single
> indirect descriptor table?
> 
> For packed virtqueue. We had:
> 
> 2.7.17 Driver Requirements: Scatter-Gather Support
> 
> A driver MUST NOT create a descriptor list longer than allowed by the
> device.
> 
> A driver MUST NOT create a descriptor list longer than the Queue Size.
> 
> 2.7.19 Driver Requirements: Indirect Descriptors
> 
> A driver MUST NOT create a descriptor chain longer than allowed by the
> device.
> 
> So it looks to me the packed part is fine.
> 
> Note that if I understand the spec correctly 2.7.17 implies 2.7.19.
> 
> Thanks

It would be quite strange for packed and split to differ here:
so for packed would you say there's no limit on # of descriptors at all?

I am guessing I just forgot to move this part from
the format specific to the common part of the spec.

This needs discussion in the TC mailing list - want to start a thread
there?



> 
> > 
> > Reported-by: Stefan Hajnoczi 
> > Signed-off-by: Connor Kuehl 
> > ---
> >   drivers/virtio/virtio_ring.c | 7 ---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 71e16b53e9c1..1bc290f9ba13 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct 
> > virtqueue *_vq,
> > head = vq->free_head;
> > +   WARN_ON_ONCE(total_sg > vq->split.vring.num);
> > +
> > if (virtqueue_use_indirect(_vq, total_sg))
> > desc = alloc_indirect_split(_vq, total_sg, gfp);
> > else {
> > desc = NULL;
> > -   WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
> > }
> > if (desc) {
> > @@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct 
> > virtqueue *_vq,
> > BUG_ON(total_sg == 0);
> > +   WARN_ON_ONCE(total_sg > vq->packed.vring.num);
> > +
> > if (virtqueue_use_indirect(_vq, total_sg))
> > return virtqueue_add_indirect_packed(vq, sgs, total_sg,
> > out_sgs, in_sgs, data, gfp);
> > @@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct 
> > virtqueue *_vq,
> > head = vq->packed.next_avail_idx;
> > avail_used_flags = vq->packed.avail_used_flags;
> > -   WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
> > -
> > desc = vq->packed.vring.desc;
> > i = head;
> > descs_used = total_sg;

Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

2021-03-21 Thread Jason Wang 



在 2021/3/18 下午9:52, Connor Kuehl 写道:

 From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
of the virtio spec:

   "A driver MUST NOT create a descriptor chain longer than the Queue
   Size of the device."

This text suggests that the warning should trigger even if
indirect descriptors are in use.



So I think at least the commit log needs some tweak.

For split virtqueue. We had:

2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table

Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total; 
this implies that loops in the descriptor chain are forbidden!


2.6.5.3.1 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than the Queue Size 
of the device.


If I understand the spec correctly, the check is only needed for a 
single indirect descriptor table?


For packed virtqueue. We had:

2.7.17 Driver Requirements: Scatter-Gather Support

A driver MUST NOT create a descriptor list longer than allowed by the 
device.


A driver MUST NOT create a descriptor list longer than the Queue Size.

2.7.19 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than allowed by the 
device.


So it looks to me the packed part is fine.

Note that if I understand the spec correctly 2.7.17 implies 2.7.19.

Thanks




Reported-by: Stefan Hajnoczi 
Signed-off-by: Connor Kuehl 
---
  drivers/virtio/virtio_ring.c | 7 ---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..1bc290f9ba13 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue 
*_vq,
  
  	head = vq->free_head;
  
+	WARN_ON_ONCE(total_sg > vq->split.vring.num);

+
if (virtqueue_use_indirect(_vq, total_sg))
desc = alloc_indirect_split(_vq, total_sg, gfp);
else {
desc = NULL;
-   WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
}
  
  	if (desc) {

@@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
  
  	BUG_ON(total_sg == 0);
  
+	WARN_ON_ONCE(total_sg > vq->packed.vring.num);

+
if (virtqueue_use_indirect(_vq, total_sg))
return virtqueue_add_indirect_packed(vq, sgs, total_sg,
out_sgs, in_sgs, data, gfp);
@@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
head = vq->packed.next_avail_idx;
avail_used_flags = vq->packed.avail_used_flags;
  
-	WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);

-
desc = vq->packed.vring.desc;
i = head;
descs_used = total_sg;

[PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

2021-03-18 Thread Connor Kuehl 
>From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
of the virtio spec:

  "A driver MUST NOT create a descriptor chain longer than the Queue
  Size of the device."

This text suggests that the warning should trigger even if
indirect descriptors are in use.

Reported-by: Stefan Hajnoczi 
Signed-off-by: Connor Kuehl 
---
 drivers/virtio/virtio_ring.c | 7 ---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..1bc290f9ba13 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue 
*_vq,
 
head = vq->free_head;
 
+   WARN_ON_ONCE(total_sg > vq->split.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
desc = alloc_indirect_split(_vq, total_sg, gfp);
else {
desc = NULL;
-   WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
}
 
if (desc) {
@@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
 
BUG_ON(total_sg == 0);
 
+   WARN_ON_ONCE(total_sg > vq->packed.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
return virtqueue_add_indirect_packed(vq, sgs, total_sg,
out_sgs, in_sgs, data, gfp);
@@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue 
*_vq,
head = vq->packed.next_avail_idx;
avail_used_flags = vq->packed.avail_used_flags;
 
-   WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
-
desc = vq->packed.vring.desc;
i = head;
descs_used = total_sg;
-- 
2.30.2