On Wed, Jun 29, 2016 at 06:53:18PM +0200, Ard Biesheuvel wrote:
> On 29 June 2016 at 18:50, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> > On 29 June 2016 at 18:45, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> >> On Wed, Jun 29, 2016 at 02:51:28PM +0200, Ard Biesheuvel wrote:
> >>> + if (!PAGE_ALIGNED(md->phys_addr) ||
> >>> + !PAGE_ALIGNED(md->num_pages << EFI_PAGE_SHIFT)) {
> >>> + /*
> >>> + * If the end address of this region is not aligned to page
> >>> + * size, the mapping is rounded up, and may end up sharing a
> >>> + * page frame with the next UEFI memory region. If we create
> >>> + * a block entry now, we may need to split it again when mapping
> >>> + * the next region, and support for that is going to be removed
> >>> + * from the MMU routines. So avoid block mappings altogether in
> >>> + * that case.
> >>> + */
> >>> + allow_block_mappings = false;
> >>> + }
> >>
> >> How common is it for large areas to have unaligned start/end? I wonder
> >> whether it's worth implementing my approach to look ahead and explicitly
> >> check the overlap with the next section instead of disabling block
> >> mappings altogether for this region.
> >>
> >
> > Very uncommon. Typically, only MMIO regions that represent NOR flash
> > are larger than a couple of pages. Taken from QEMU:
>
> RT_Code : 640 Pages (2,621,440 Bytes)
> RT_Data : 880 Pages (3,604,480 Bytes)
>
> so all RT_Code regions *combined* are 2.5 MB in total, and all RT_Data
> regions 3.5 MB. Ideally, they are grouped together, but in reality,
> there are always a couple of regions of each type, so there is little
> to gain here from using block mappings
Is this representative for real platforms?
What about efifb and reserved regions?
My (x86) Lenovo workstation has one 64MB and one 16MB Runtime/Uncached
MMIO region. As well as a 3MB and a 4MB RT_Data one.
/
Leif
--
To unsubscribe from this list: send the line "unsubscribe linux-efi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
