>>> On 11.09.18 at 11:34, <[email protected]> wrote:
>> From: Jan Beulich [mailto:[email protected]]
>> Sent: 07 September 2018 12:01
>>
>> >>> On 23.08.18 at 11:47, <[email protected]> wrote:
>> > This patch adds an iommu_op to allow the domain IOMMU reserved
>> ranges to be
>> > queried by the guest.
>> >
>> > NOTE: The number of reserved ranges is determined by system firmware,
>> in
>> > conjunction with Xen command line options, and is expected to be
>> > small. Thus, to avoid over-complicating the code, there is no
>> > pre-emption check within the operation.
>>
>> Hmm, RMRRs reportedly can cover a fair part of (the entire?) frame
>> buffer of a graphics device.
>
> That would still be phrased as a single range though, right?
Ah, yes, indeed.
>> > iommu_op(&nat);
>> >
>> > + status = nat.status;
>> > +
>> > +#define XLAT_iommu_op_query_reserved_HNDL_ranges(_d_, _s_)
>> \
>> > + do \
>> > + { \
>> > + if ( !compat_handle_is_null((_d_)->ranges) ) \
>> > + { \
>> > + unsigned int *nr_entries = COMPAT_ARG_XLAT_VIRT_BASE; \
>> > + compat_iommu_reserved_range_t *ranges = \
>> > + (void *)(nr_entries + 1); \
>> > + unsigned int nr = \
>> > + min_t(unsigned int, (_d_)->nr_entries, *nr_entries); \
>> > + \
>> > + if ( __copy_to_compat_offset((_d_)->ranges, 0, ranges, nr) ) \
>> > + status = -EFAULT; \
>> > + } \
>> > + } while (false)
>> > +
>> > XLAT_iommu_op(&cmp, &nat);
>> >
>> > + /* status will have been modified if __copy_to_compat_offset() failed
>> */
>> > + cmp.status = status;
>> > +
>> > +#undef XLAT_iommu_op_query_reserved_HNDL_ranges
>> > +
>> > if ( __copy_field_to_compat(compat_handle_cast(buf->h,
>> > compat_iommu_op_t),
>> > &cmp, status) )
>> > return -EFAULT;
>> >
>> > +#undef XLAT_iommu_op_u_query_reserved
>> > +
>> > return 0;
>> > }
>>
>> It's somehow more evident here, but I think even on the native path
>> the nr_entries field doesn't get copied back despite it being an OUT.
>
> Indeed. It would be so much simpler just to copy back the entire buf to
> avoid the need to special-case this for each op.
In case of such complications I view doing so as perfectly legitimate. It's
just that in cases where copying a single field is obviously easy and
sufficient that I suggest/request that only that one field be copied.
Jan
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