Re: [dpdk-stable] [PATCH 1/7] vhost: fix virtqueues metadata allocation

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Chenbon

On 10/21/20 1:10 PM, Xia, Chenbo wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Tuesday, October 20, 2020 1:34 AM
>> To: dev@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; amorenoz@redhat.com
>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; stable@dpdk.org
>> Subject: [PATCH 1/7] vhost: fix virtqueues metadata allocation
>>
>> The Vhost-user backend implementation assumes there will be
>> no holes in the device's array of virtqueues metadata
>> pointers.
>>
>> It can happen though, and would cause segmentation faults,
>> memory leaks or undefined behaviour.
> 
> Could I ask when will this happen? 
> 
> When QEMU does not configure all virtqueues? I'm not very sure.
> Could you point that out for me?

It has been reported by our QE when doing reconnect with multiqueue with
vIOMMU enabled:
https://bugzilla.redhat.com/show_bug.cgi?id=1880299

Regards,
Maxime

> Thanks!
> Chenbo
> 
>>
>> This patch keep the assumption that there is no holes in this
>> array, and allocate all uninitialized virtqueues metadata up
>> to requested index.
>>
>> Fixes: 160cbc815b41 ("vhost: remove a hack on queue allocation")
>> Cc: stable@dpdk.org
>>
>> Suggested-by: Adrian Moreno <amorenoz@redhat.com>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>  lib/librte_vhost/vhost.c | 33 ++++++++++++++++++++-------------
>>  1 file changed, 20 insertions(+), 13 deletions(-)
>>
>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
>> index 6068c38ec6..0c9ba3b3af 100644
>> --- a/lib/librte_vhost/vhost.c
>> +++ b/lib/librte_vhost/vhost.c
>> @@ -579,22 +579,29 @@ int
>>  alloc_vring_queue(struct virtio_net *dev, uint32_t vring_idx)
>>  {
>>  	struct vhost_virtqueue *vq;
>> +	uint32_t i;
>>
>> -	vq = rte_malloc(NULL, sizeof(struct vhost_virtqueue), 0);
>> -	if (vq == NULL) {
>> -		VHOST_LOG_CONFIG(ERR,
>> -			"Failed to allocate memory for vring:%u.\n", vring_idx);
>> -		return -1;
>> -	}
>> +	/* Also allocate holes, if any, up to requested vring index. */
>> +	for (i = 0; i <= vring_idx; i++) {
>> +		if (dev->virtqueue[i])
>> +			continue;
>>
>> -	dev->virtqueue[vring_idx] = vq;
>> -	init_vring_queue(dev, vring_idx);
>> -	rte_spinlock_init(&vq->access_lock);
>> -	vq->avail_wrap_counter = 1;
>> -	vq->used_wrap_counter = 1;
>> -	vq->signalled_used_valid = false;
>> +		vq = rte_malloc(NULL, sizeof(struct vhost_virtqueue), 0);
>> +		if (vq == NULL) {
>> +			VHOST_LOG_CONFIG(ERR,
>> +				"Failed to allocate memory for vring:%u.\n", i);
>> +			return -1;
>> +		}
>> +
>> +		dev->virtqueue[i] = vq;
>> +		init_vring_queue(dev, vring_idx);
>> +		rte_spinlock_init(&vq->access_lock);
>> +		vq->avail_wrap_counter = 1;
>> +		vq->used_wrap_counter = 1;
>> +		vq->signalled_used_valid = false;
>> +	}
>>
>> -	dev->nr_vring += 1;
>> +	dev->nr_vring = RTE_MAX(dev->nr_vring, vring_idx + 1);
>>
>>  	return 0;
>>  }
>> --
>> 2.26.2
>