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

[Jason Wang]

On 2018å07æ04æ 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@xxxxxxxxxx>
> > ---
> >   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.

Thanks