Re: [Xen-devel] [PATCH 6/7] x86: add iommu_op to query reserved ranges

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.03.18 at 16:36, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 19 March 2018 15:14
>> 
>> >>> On 12.02.18 at 11:47, <paul.durrant@xxxxxxxxxx> wrote:
>> > --- a/xen/arch/x86/iommu_op.c
>> > +++ b/xen/arch/x86/iommu_op.c
>> > @@ -22,6 +22,58 @@
>> >  #include <xen/event.h>
>> >  #include <xen/guest_access.h>
>> >  #include <xen/hypercall.h>
>> > +#include <xen/iommu.h>
>> > +
>> > +struct get_rdm_ctxt {
>> > +    unsigned int max_entries;
>> > +    unsigned int nr_entries;
>> > +    XEN_GUEST_HANDLE(xen_iommu_reserved_region_t) regions;
>> > +};
>> > +
>> > +static int get_rdm(xen_pfn_t start, xen_ulong_t nr, u32 id, void *arg)
>> > +{
>> > +    struct get_rdm_ctxt *ctxt = arg;
>> > +
>> > +    if ( ctxt->nr_entries < ctxt->max_entries )
>> > +    {
>> > +        xen_iommu_reserved_region_t region = {
>> > +            .start_bfn = start,
>> > +            .nr_frames = nr,
>> > +        };
>> > +
>> > +        if ( copy_to_guest_offset(ctxt->regions, ctxt->nr_entries, 
>> > &region,
>> > +                                  1) )
>> > +            return -EFAULT;
>> > +    }
>> > +
>> > +    ctxt->nr_entries++;
>> > +
>> > +    return 1;
>> > +}
>> > +
>> > +static int iommuop_query_reserved(struct
>> xen_iommu_op_query_reserved *op)
>> > +{
>> > +    struct get_rdm_ctxt ctxt = {
>> > +        .max_entries = op->nr_entries,
>> > +        .regions = op->regions,
>> > +    };
>> > +    int rc;
>> > +
>> > +    if (op->pad != 0)
>> > +        return -EINVAL;
>> > +
>> > +    rc = iommu_get_reserved_device_memory(get_rdm, &ctxt);
>> > +    if ( rc )
>> > +        return rc;
>> > +
>> > +    /* Pass back the actual number of reserved regions */
>> > +    op->nr_entries = ctxt.nr_entries;
>> > +
>> > +    if ( ctxt.nr_entries > ctxt.max_entries )
>> > +        return -ENOBUFS;
>> > +
>> > +    return 0;
>> > +}
>> 
>> One more note here: As it looks we can only hope there won't be
>> too many RMRRs, as the number of entries that can be requested
>> here is basically unbounded.
>> 
> 
> The caller has to be able to allocate a buffer large enough but, yes there 
> is no explicit limit. I'll add pre-empt checks.

Thing is - preempt check probably won't be easy with the way
iommu_get_reserved_device_memory() works.

Jan


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