Re: [dpdk-dev] [PATCH] vhost: fix invalid use of stored last used index

["Ling, WeiX" <weix.ling@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Monday, May 17, 2021 03:38 PM
> To: Balazs Nemeth <bnemeth@redhat.com>; dev@dpdk.org; Ling, WeiX
> <weix.ling@intel.com>
> Subject: Re: [dpdk-dev] [PATCH] vhost: fix invalid use of stored last used
> index
> 
> Hi Ling,
> 
> 
> On 5/14/21 6:02 PM, Balazs Nemeth wrote:
> > The optimization introduced by commit d18db8049c7c ("vhost: read last
> > used index once") didn't account for the fact that
> > vhost_flush_enqueue_shadow_packed increments the last_used_idx. For
> > this reason, store last_used_idx after the potential call to
> > vhost_flush_enqueue_shadow_packed.
> >
> > Fixes: d18db8049c7c ("vhost: read last used index once")
> > Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
> > ---
> >  lib/vhost/virtio_net.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c index
> > abfd67d38c..8da8a86a10 100644
> > --- a/lib/vhost/virtio_net.c
> > +++ b/lib/vhost/virtio_net.c
> > @@ -218,14 +218,17 @@ vhost_flush_enqueue_batch_packed(struct
> > virtio_net *dev,  {
> >  	uint16_t i;
> >  	uint16_t flags;
> > -	uint16_t last_used_idx = vq->last_used_idx;
> > -	struct vring_packed_desc *desc_base = &vq-
> >desc_packed[last_used_idx];
> > +	uint16_t last_used_idx;
> > +	struct vring_packed_desc *desc_base;
> >
> >  	if (vq->shadow_used_idx) {
> >  		do_data_copy_enqueue(dev, vq);
> >  		vhost_flush_enqueue_shadow_packed(dev, vq);
> >  	}
> >
> > +	last_used_idx = vq->last_used_idx;
> > +	desc_base = &vq->desc_packed[last_used_idx];
> > +
> >  	flags = PACKED_DESC_ENQUEUE_USED_FLAG(vq-
> >used_wrap_counter);
> >
> >  	vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> >
> 
> Could you please confirm the patch fixes the issue you reported?
> 
> Thanks,
> Maxime

Hi Maxime,

Apply your patch https://patches.dpdk.org/project/dpdk/patch/83fa6253725a7bc69bccb7897f380422354a2898.1621008025.git.bnemeth@redhat.com/ based on DPDK-21.05-rc3(7989b7e7da9b), tested PASSED.

Regards,
Ling Wei