Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Ard Biesheuvel <ardb@kernel.org>]

On Thu, 15 Oct 2020 at 12:31, Lorenzo Pieralisi
<lorenzo.pieralisi@arm.com> wrote:
>
> On Wed, Oct 14, 2020 at 09:12:09PM +0200, Nicolas Saenz Julienne wrote:
>
> [...]
>
> > +unsigned int __init acpi_iort_get_zone_dma_size(void)
> > +{
> > +     struct acpi_table_iort *iort;
> > +     struct acpi_iort_node *node, *end;
> > +     acpi_status status;
> > +     u8 limit = 32;
> > +     int i;
> > +
> > +     if (acpi_disabled)
> > +             return limit;
> > +
> > +     status = acpi_get_table(ACPI_SIG_IORT, 0,
> > +                             (struct acpi_table_header **)&iort);
> > +     if (ACPI_FAILURE(status))
> > +             return limit;
> > +
> > +     node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> > +     end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> > +
> > +     for (i = 0; i < iort->node_count; i++) {
> > +             if (node >= end)
> > +                     break;
> > +
> > +             switch (node->type) {
> > +                     struct acpi_iort_named_component *ncomp;
> > +                     struct acpi_iort_root_complex *rc;
> > +
> > +             case ACPI_IORT_NODE_NAMED_COMPONENT:
> > +                     ncomp = (struct acpi_iort_named_component *)node->node_data;
> > +                     if (ncomp->memory_address_limit)
> > +                             limit = min(limit, ncomp->memory_address_limit);
> > +                     break;
> > +
> > +             case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> > +                     rc = (struct acpi_iort_root_complex *)node->node_data;
> > +                     if (rc->memory_address_limit)
>
> You need to add a node revision check here, see rc_dma_get_range() in
> drivers/acpi/arm64/iort.c, otherwise we may be reading junk data
> in older IORT tables - acpica structures are always referring to the
> latest specs.
>

Indeed - apologies for not mentioning that when handing over the patch.

Also, we could use min_not_zero() here instead of the if ()