Re: [PATCH V2 2/3] xen/arm: Add handling of extended regions for Dom0

[Stefano Stabellini <sstabellini@kernel.org>]

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On Fri, 17 Sep 2021, Oleksandr wrote:
> > > +
> > > +    dt_dprintk("Find unallocated memory for extended regions\n");
> > > +
> > > +    unalloc_mem = rangeset_new(NULL, NULL, 0);
> > > +    if ( !unalloc_mem )
> > > +        return -ENOMEM;
> > > +
> > > +    /* Start with all available RAM */
> > > +    for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
> > > +    {
> > > +        start = bootinfo.mem.bank[i].start;
> > > +        end = bootinfo.mem.bank[i].start + bootinfo.mem.bank[i].size - 1;
> > > +        res = rangeset_add_range(unalloc_mem, start, end);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove RAM assigned to Dom0 */
> > > +    for ( i = 0; i < assign_mem->nr_banks; i++ )
> > > +    {
> > > +        start = assign_mem->bank[i].start;
> > > +        end = assign_mem->bank[i].start + assign_mem->bank[i].size - 1;
> > > +        res = rangeset_remove_range(unalloc_mem, start, end);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove reserved-memory regions */
> > > +    for ( i = 0; i < bootinfo.reserved_mem.nr_banks; i++ )
> > > +    {
> > > +        start = bootinfo.reserved_mem.bank[i].start;
> > > +        end = bootinfo.reserved_mem.bank[i].start +
> > > +            bootinfo.reserved_mem.bank[i].size - 1;
> > > +        res = rangeset_remove_range(unalloc_mem, start, end);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove grant table region */
> > > +    start = kinfo->gnttab_start;
> > > +    end = kinfo->gnttab_start + kinfo->gnttab_size - 1;
> > > +    res = rangeset_remove_range(unalloc_mem, start, end);
> > > +    if ( res )
> > > +    {
> > > +        printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> > > +               start, end);
> > > +        goto out;
> > > +    }
> > > +
> > > +    start = EXT_REGION_START;
> > > +    end = min((1ULL << p2m_ipa_bits) - 1, EXT_REGION_END);
> > > +    res = rangeset_report_ranges(unalloc_mem, start, end,
> > > +                                 add_ext_regions, ext_regions);
> > > +    if ( res )
> > > +        ext_regions->nr_banks = 0;
> > > +    else if ( !ext_regions->nr_banks )
> > > +        res = -ENOENT;
> > > +
> > > +out:
> > > +    rangeset_destroy(unalloc_mem);
> > > +
> > > +    return res;
> > > +}
> > > +
> > > +static int __init find_memory_holes(const struct kernel_info *kinfo,
> > > +                                    struct meminfo *ext_regions)
> > > +{
> > > +    struct dt_device_node *np;
> > > +    struct rangeset *mem_holes;
> > > +    paddr_t start, end;
> > > +    unsigned int i;
> > > +    int res;
> > > +
> > > +    dt_dprintk("Find memory holes for extended regions\n");
> > > +
> > > +    mem_holes = rangeset_new(NULL, NULL, 0);
> > > +    if ( !mem_holes )
> > > +        return -ENOMEM;
> > > +
> > > +    /* Start with maximum possible addressable physical memory range */
> > > +    start = EXT_REGION_START;
> > > +    end = min((1ULL << p2m_ipa_bits) - 1, EXT_REGION_END);
> > > +    res = rangeset_add_range(mem_holes, start, end);
> > > +    if ( res )
> > > +    {
> > > +        printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> > > +               start, end);
> > > +        goto out;
> > > +    }
> > > +
> > > +    /* Remove all regions described by "reg" property (MMIO, RAM, etc) */
> > 
> > Well... The loop below is not going to handle all the regions described in
> > the property "reg". Instead, it will cover a subset of "reg" where the
> > memory is addressable.
> 
> As I understand, we are only interested in subset of "reg" where the memory is
> addressable.
> 
> 
> > 
> > 
> > You will also need to cover "ranges" that will describe the BARs for the PCI
> > devices.
> Good point.

Yes, very good point!


> Could you please clarify how to recognize whether it is a PCI
> device as long as PCI support is not merged? Or just to find any device nodes
> with non-empty "ranges" property
> and retrieve addresses?

Normally any bus can have a ranges property with the aperture and
possible address translations, including /amba (compatible =
"simple-bus"). However, in these cases dt_device_get_address already
takes care of it, see xen/common/device_tree.c:dt_device_get_address.

The PCI bus is special for 2 reasons:
- the ranges property has a different format
- the bus is hot-pluggable

So I think the only one that we need to treat specially is PCI.

As far as I am aware PCI is the only bus (or maybe just the only bus
that we support?) where ranges means the aperture.