lkml.org 
[lkml]   [2021]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size
From
Date

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 <stefanha@redhat.com>
>>> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
>>> ---
>>> 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;

\
 
 \ /
  Last update: 2021-03-23 03:40    [W:0.085 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site