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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

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?

Jan


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