On 29 June 2016 at 18:45, Catalin Marinas [off-list ref] wrote:

On Wed, Jun 29, 2016 at 02:51:28PM +0200, Ard Biesheuvel wrote:

quoted

+     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: