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arch: enable MPU Gap filling by default in build without user mode

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When we build without support for user mode, we do not need
a large number of MPU regions, so we should not allow having
MPU_GAP_FILLING unset. This would allow PRIV code execute from
SRAM, which is an unnecessary compromise on ARMv8-M builds
without USERSPACE support. We update the Kconfig dependencies
and add a sentence for clarification.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
This commit is contained in:
Ioannis Glaropoulos 2019-11-11 12:46:31 +01:00 • committed by Alberto Escolar
commit 98201228ee
1 changed files with 4 additions and 2 deletions
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6
arch/Kconfig
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@ -454,7 +454,7 @@ config MPU_REQUIRES_NON_OVERLAPPING_REGIONS
config MPU_GAP_FILLING config MPU_GAP_FILLING
bool "Force MPU to be filling in background memory regions" bool "Force MPU to be filling in background memory regions"
depends on MPU_REQUIRES_NON_OVERLAPPING_REGIONS depends on MPU_REQUIRES_NON_OVERLAPPING_REGIONS
depends on USERSPACE default y if !USERSPACE
help help
This Kconfig option instructs the MPU driver to enforce This Kconfig option instructs the MPU driver to enforce
a full kernel SRAM partitioning, when it programs the a full kernel SRAM partitioning, when it programs the
@ -466,7 +466,9 @@ config MPU_GAP_FILLING
Notes: Notes:
An increased number of MPU regions should only be required, An increased number of MPU regions should only be required,
when building with USERSPACE support. when building with USERSPACE support. As a result, when we
build without USERSPACE support, gap filling should always
be required.
When the option is switched off, access to memory areas not When the option is switched off, access to memory areas not
covered by explicit MPU regions is restricted to privileged covered by explicit MPU regions is restricted to privileged