Re: [Xen-devel] [PATCH RFC v1 56/74] xen/pvshim: add grant table operations

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jan 10, 2018 at 12:28:27AM -0700, Jan Beulich wrote:
> >>> On 09.01.18 at 19:34, <roger.pau@xxxxxxxxxx> wrote:
> > On Mon, Jan 08, 2018 at 10:19:39AM -0700, Jan Beulich wrote:
> >> >>> On 04.01.18 at 14:06, <wei.liu2@xxxxxxxxxx> wrote:
> >> > +    {
> >> > +        struct gnttab_query_size op;
> >> > +        int rc;
> >> > +
> >> > +        if ( unlikely(copy_from_guest(&op, uop, 1)) )
> >> > +        {
> >> > +            rc = -EFAULT;
> >> > +            break;
> >> > +        }
> >> > +
> >> > +        rc = xen_hypercall_grant_table_op(GNTTABOP_query_size, &op, 
> >> > count);
> >> > +        if ( rc )
> >> > +            break;
> >> > +
> >> > +        if ( copy_to_guest(uop, &op, 1) )
> >> 
> >> __copy_to_guest() (assuming this coping in and out is necessary
> >> in the first place).
> > 
> > I guess this could be bypassed by just using uop instead of op in the
> > hypercall?
> 
> That's my impression, but you doing the copying made me assume
> you might have found a case where things don't work without
> copying.

No, just didn't realize I could do it that way. gnttab_query_size
doesn't require any compat code AFAICT, so it should work fine.

Thanks, Roger.

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