linux-kernel - Re: [PATCH net-next 8/8] vhost: event suppression for packed ring

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Message-ID: <20180704081356.GB9287@wei-ubt>
Date:   Wed, 4 Jul 2018 16:13:56 +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, tiwei.bie@...el.com,
        maxime.coquelin@...hat.com, jfreimann@...hat.com
Subject: Re: [PATCH net-next 8/8] vhost: event suppression for packed ring

On Wed, Jul 04, 2018 at 01:23:18PM +0800, Jason Wang wrote:
> 
> 
> On 2018年07月04日 12:13, Wei Xu wrote:
> >On Tue, Jul 03, 2018 at 01:38:04PM +0800, Jason Wang wrote:
> >>This patch introduces support for event suppression. This is done by
> >>have a two areas: device area and driver area. One side could then try
> >>to disable or enable (delayed) notification from other side by using a
> >>boolean hint or event index interface in the areas.
> >>
> >>For more information, please refer Virtio spec.
> >>
> >>Signed-off-by: Jason Wang<jasowang@...hat.com>
> >>---
> >>  drivers/vhost/vhost.c | 191 ++++++++++++++++++++++++++++++++++++++++++++++----
> >>  drivers/vhost/vhost.h |  10 ++-
> >>  2 files changed, 185 insertions(+), 16 deletions(-)
> >>
> >>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >>index 0f3f07c..cccbc82 100644
> >>--- a/drivers/vhost/vhost.c
> >>+++ b/drivers/vhost/vhost.c
> >>@@ -1115,10 +1115,15 @@ static int vq_access_ok_packed(struct vhost_virtqueue *vq, unsigned int num,
> >>  			       struct vring_used __user *used)
> >>  {
> >>  	struct vring_desc_packed *packed = (struct vring_desc_packed *)desc;
> >>+	struct vring_packed_desc_event *driver_event =
> >>+		(struct vring_packed_desc_event *)avail;
> >>+	struct vring_packed_desc_event *device_event =
> >>+		(struct vring_packed_desc_event *)used;
> >>-	/* TODO: check device area and driver area */
> >>  	return access_ok(VERIFY_READ, packed, num * sizeof(*packed)) &&
> >>-	       access_ok(VERIFY_WRITE, packed, num * sizeof(*packed));
> >>+	       access_ok(VERIFY_WRITE, packed, num * sizeof(*packed)) &&
> >R/W parameter doesn't make sense to most architectures and the comment in x86
> >says WRITE is a superset of READ, is it possible to converge them here?
> >
> >/**
> >  * access_ok: - Checks if a user space pointer is valid
> >  * @type: Type of access: %VERIFY_READ or %VERIFY_WRITE.  Note that
> >  *        %VERIFY_WRITE is a superset of %VERIFY_READ - if it is safe
> >  *        to write to a block, it is always safe to read from it.
> >  * @addr: User space pointer to start of block to check
> >  * @size: Size of block to check
> >  *
> >  * Context: User context only. This function may sleep if pagefaults are
> >  *          enabled.
> >  *
> >  * Checks if a pointer to a block of memory in user space is valid.
> >  *
> >  * Returns true (nonzero) if the memory block may be valid, false (zero)
> >  * if it is definitely invalid.
> >  *
> >  * Note that, depending on architecture, this function probably just
> >  * checks that the pointer is in the user space range - after calling
> >  * this function, memory access functions may still return -EFAULT.
> >  */
> >#define access_ok(type, addr, size)
> >......
> >
> >Thanks,
> >Wei
> >
> 
> Well, this is a question that beyond the scope of this patch.
> 
> My understanding is we should keep it unless type was meaningless on all
> archs.

No problem, go ahead.

Wei

> 
> Thanks
>