linux-kernel - Re: [RFC V4 PATCH 7/8] vhost: packed ring support

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Message-ID: <20180523071727.GA13373@wei-ubt>
Date:   Wed, 23 May 2018 15:17:27 +0800
From:   Wei Xu <wexu@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jfreimann@...hat.com,
        tiwei.bie@...el.com
Subject: Re: [RFC V4 PATCH 7/8] vhost: packed ring support

On Wed, May 23, 2018 at 09:39:28AM +0800, Jason Wang wrote:
> 
> 
> On 2018年05月23日 00:54, Wei Xu wrote:
> >On Wed, May 16, 2018 at 08:32:20PM +0800, Jason Wang wrote:
> >>Signed-off-by: Jason Wang <jasowang@...hat.com>
> >>---
> >>  drivers/vhost/net.c   |   3 +-
> >>  drivers/vhost/vhost.c | 539 ++++++++++++++++++++++++++++++++++++++++++++++----
> >>  drivers/vhost/vhost.h |   8 +-
> >>  3 files changed, 513 insertions(+), 37 deletions(-)
> >>
> >>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >>index 8304c30..f2a0f5b 100644
> >>--- a/drivers/vhost/vhost.c
> >>+++ b/drivers/vhost/vhost.c
> >>@@ -1358,6 +1382,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
> >>  			break;
> >>  		}
> >>  		vq->last_avail_idx = s.num;
> >>+		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> >>+			vq->avail_wrap_counter = s.num >> 31;
> >>  		/* Forget the cached index value. */
> >>  		vq->avail_idx = vq->last_avail_idx;
> >>  		break;
> >>@@ -1366,6 +1392,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
> >>  		s.num = vq->last_avail_idx;
> >>  		if (copy_to_user(argp, &s, sizeof s))
> >>  			r = -EFAULT;
> >>+		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> >>+			s.num |= vq->avail_wrap_counter << 31;
> >>  		break;
> >>  	case VHOST_SET_VRING_ADDR:
> >>  		if (copy_from_user(&a, argp, sizeof a)) {
> >'last_used_idx' also needs to be saved/restored here.
> >
> >I have figured out the root cause of broken device after reloading
> >'virtio-net' module, all indices have been reset for a reloading but
> >'last_used_idx' is not properly reset in this case. This confuses
> >handle_rx()/tx().
> >
> >Wei
> >
> 
> Good catch, so we probably need a new ioctl to sync between qemu and vhost.
> 
> Something like VHOST_SET/GET_USED_BASE.

Sure, or can we expand 'vhost_vring_state' to keep them done in a bunch?

> 
> Thanks
>