Re: [Xen-devel] [PATCH v11 10/11] common: add a new mappable resource type: XENMEM_resource_grant_table

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 17 October 2017 10:06
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; sstabellini@xxxxxxxxxx; xen-
> devel@xxxxxxxxxxxxxxxxxxxx; konrad.wilk@xxxxxxxxxx; Tim (Xen.org)
> <tim@xxxxxxx>
> Subject: RE: [PATCH v11 10/11] common: add a new mappable resource type:
> XENMEM_resource_grant_table
> 
> >>> On 17.10.17 at 10:30, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:jbeulich@xxxxxxxx]
> >> Sent: 17 October 2017 07:43
> >> >>> Paul Durrant <paul.durrant@xxxxxxxxxx> 10/12/17 6:28 PM >>>
> >> >+int gnttab_get_grant_frame(struct domain *d, unsigned long idx,
> >> >+                           mfn_t *mfn)
> >> >+{
> >> >+    struct grant_table *gt = d->grant_table;
> >> >+    int rc;
> >> >+
> >> >+    /* write lock required as version may change and/or table may grow
> */
> >> >+    grant_write_lock(gt);
> >> >+
> >> >+    rc = (gt->gt_version == 2 &&
> >> >+          idx > XENMAPIDX_grant_table_status) ?
> >>
> >> I don't understand this check - why does XENMAPIDX_grant_table_status
> >> matter here at all? Same in gnttab_get_status_frame() then.
> >>
> >
> > Well, the current legal range of grant table frames for v2 is 0 - (1 <<
> > XENMAPIDX_grant_table_status) whereas it appears that for v1 there is no
> > limit. As for status frames, they are a v2-only concept but I agree that the
> > range check there is wrong.
> 
> I don't think the range limitation from the other interface should
> impose any restriction for this new one.

Ok. I'll drop the check.

> 
> Oh, one other thing I only notice now - could you please also
> attach a brief comment to the array that you grow to 32
> entries making clear that this is a pretty arbitrary choice?
> 

Sure.

  Paul

> Jan


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