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

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 19 March 2018 15:14
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>; Wei Liu
> <wei.liu2@citrix.com>; George Dunlap <George.Dunlap@citrix.com>; Ian
> Jackson <Ian.Jackson@citrix.com>; Stefano Stabellini
> <sstabellini@kernel.org>; xen-devel@lists.xenproject.org; Konrad Rzeszutek
> Wilk <konrad.wilk@oracle.com>; Tim (Xen.org) <tim@xen.org>
> Subject: Re: [PATCH 6/7] x86: add iommu_op to query reserved ranges
> 
> >>> On 12.02.18 at 11:47, <paul.durrant@citrix.com> 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.

  Paul

> Jan


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