[PATCH v2 07/12] ARM: split off core mapping logic from create_mapping

On 16 November 2015 at 19:55, Russell King - ARM Linux
[off-list ref] wrote:

On Mon, Nov 16, 2015 at 07:32:32PM +0100, Ard Biesheuvel wrote:

quoted

In order to be able to reuse the core mapping logic of create_mapping
for mapping the UEFI Runtime Services into a private set of page tables,
split it off from create_mapping() into a separate function
__create_mapping which we will wire up in a subsequent patch.

I'm slightly worried about this.  Generally, these functions setup
global mappings.  If you're wanting to have a private set of page
tables for UEFI, and those private page tables contain global
mappings which are different from the mappings in the kernel's page
tables, then you need careful break-TLBflush-make handling when
switching from the kernel's page tables to the private UEFI ones,
and vice versa.

Has this aspect been considered?

Yes. The UEFI mappings are all below 1 GB, and the top kernel end is
reused as we do for ordinary userland page tables. The switch to the
UEFI page tables performs a full TLB flush. What it does not do is
break before make, as far as I can tell, so any pointers regarding how
to implement that would be appreciated (this is implemented in 11/12)

-- 
Ard.