[RFC PATCH 0/7]

[Patrick Delaunay]

arm: cache: cp15: don't map reserved region with no-map property

Hi,

On STM32MP15x platform we can use OP-TEE, loaded in DDR in a region protected
by a firewall. This region is reserved in device with "no-map" property.

But sometime the platform boot failed in U-boot on a Cortex A7 access to this
region (depending of the binary and the issue can change with compiler version or
with code alignment), then the firewall raise a error, for example:

E/TC:0   tzc_it_handler:19 TZC permission failure
E/TC:0   dump_fail_filter:420 Permission violation on filter 0
E/TC:0   dump_fail_filter:425 Violation @0xde5c6bf0, non-secure privileged read, AXI ID 5c0
E/TC:0   Panic

After investigation, the forbidden access is a speculative request performed by
the Cortex A7 because all the DDR is mapped as MEMORY with CACHEABLE property.

The issue is solved only when the region reserved by OP-TEE is no more mapped
in U-Boot (mapped as DEVICE/NON-CACHEABLE wasn't enough) as it is already done
in Linux kernel.

I think that can be a general issue for ARM architecture: the no-map tag in
device should be respected by U-boot, so I propose a  generic solution in
arm/lib/cache-cp15.c:dram_bank_mmu_setup().

This RFC serie is composed by 7 patches
- 1..4/7: preliminary steps to support flags in library in lmb
  (as it is done in memblock.c in Linux)
- 5/7: unitary test on the added feature in lmb lib
- 6/7: save the no-map flags in lmb when the device tree is parsed
- 7/7: update the generic behavior for "no-map" region in
       arm/lib/cache-cp15.c::dram_bank_mmu_setup()

I can change this last patch if it is required by other ARM architecture;
it is a weak function so I can avoid to map the region with "no-map"
property in device tree only for STM32MP architecture
(in arch/arm/mach-stm32mp/cpu.c).

See also [1] which handle same speculative access on armv8 for area
with Executable attribute.

[1] http://patchwork.ozlabs.org/project/uboot/patch/20200903000106.5016-1-marek.bykowski@gmail.com/

Regards
Patrick


Patrick Delaunay (7):
  lmb: Add support of flags for no-map properties
  lmb: add lmb_is_reserved_flags
  lmb: remove lmb_region.size
  lmb: add lmb_dump_region() function
  test: lmb: add test for lmb_reserve_flags
  image-fdt: save no-map parameter of reserve-memory
  arm: cache: cp15: don't map the reserved region with no-map property

 arch/arm/include/asm/system.h |   3 +
 arch/arm/lib/cache-cp15.c     |  17 +++++-
 common/image-fdt.c            |  23 +++++---
 include/lmb.h                 |  22 +++++++-
 lib/lmb.c                     | 100 +++++++++++++++++++++++-----------
 test/lib/lmb.c                |  89 ++++++++++++++++++++++++++++++
 6 files changed, 210 insertions(+), 44 deletions(-)

-- 
2.17.1