Re: [Xen-devel] [v5][PATCH 03/10] xen:x86: define a new hypercall to get RMRR mappings

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/9/2 18:15, Jan Beulich wrote:
> > > > On 02.09.14 at 11:59, <tiejun.chen@xxxxxxxxx> wrote:
> > So could you take a look at the follows?
> I'm sorry, but this is a nightmare. Do you know what the term
> "callback" means?
I don't know how to handle this in the hypercall case.

> > Then when call the hypercall,
> >
> > +    case XENMEM_reserved_device_memory_map:
> > +    {
> > +        struct xen_mem_reserved_device_memory *xmrdm = NULL;
> > +        struct xen_mem_reserved_device_memory_map xmrdmm;
> > +        XEN_GUEST_HANDLE(xen_mem_reserved_device_memory_t) buffer;
> > +        XEN_GUEST_HANDLE_PARAM(xen_mem_reserved_device_memory_t) buffer_param;
> > +        const struct iommu_ops *ops = iommu_get_ops();
> > +        unsigned int nr_entries = 0;
> > +        unsigned int i = 0;
> > +
> > +        xmrdm = ops->get_device_reserved_memory(&nr_entries);
Do we still need this iommu_ops somewhere else?

> > +        if ( !nr_entries )
Do we still need this 'nr_entries' here?

> > +            return -ENOENT;
> > +        if ( nr_entries < 0 )
> > +            return -EFAULT;
> > +
> > +        if ( copy_from_guest(&xmrdmm, arg, 1) )
> > +            return -EFAULT;
> > +
> > +        if ( xmrdmm.nr_entries < nr_entries )
> > +        {
> > +            xmrdmm.nr_entries = nr_entries;
> > +            if ( copy_to_guest(arg, &xmrdmm, 1) )
> > +                return -EFAULT;
> > +            return -ENOBUFS;
> > +        }
> > +
> > +        buffer_param = guest_handle_cast(xmrdmm.buffer,
> > +                                         xen_mem_reserved_device_memory_t);
> > +        buffer = guest_handle_from_param(buffer_param,
> > +                                         xen_mem_reserved_device_memory_t);
> > +        if ( !guest_handle_okay(buffer, xmrdmm.nr_entries) )
> > +            return -EFAULT;
> > +
> > +        for ( i = 0; i < nr_entries; i++ )
> > +        {
> > +            if ( copy_to_guest_offset(buffer, i, xmrdm + i, 1) )
> > +                return -EFAULT;
> > +        }
> The equivalent of this loop would move into the new (abstracted at
> the IOMMU level) VT-d function. Out of that loop you'd call the
> callback passed from here once per iteration; the called function
> would take care of storing the needed information and advancing a
> private counter. No memory allocation, and no VT-d specific
> knowledge required in generic code.
>
> Jan
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