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x86: update X86_MMU_PAGE_POOL_PAGES documentation

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Help users understand how this should be tuned. Rather than
guessing wildly, set the default to 0. This needs to be tuned
on a per-board, per-application basis anyway.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2020-10-23 16:01:53 -07:00 committed by Anas Nashif
parent 0dae74e4a5
commit 8e5114b370
1 changed files with 18 additions and 4 deletions
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22
arch/x86/Kconfig
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@ -192,12 +192,26 @@ config X86_MMU
config X86_MMU_PAGE_POOL_PAGES
int "Number of pages to reserve for building page tables"
default 17
default 0
depends on X86_MMU
help
Building page tables at boot requires a pool of free memory pages
to construct it. This can't be derived at build time, tune this
to your SoC's specific memory map.
Define the number of pages in the pool used to allocate page table
data structures at runtime.
Pages might need to be drawn from the pool during memory mapping
operations, unless the address space has been completely pre-allocated.
Pages will need to drawn from the pool to initialize memory domains.
This does not include the default memory domain if KPTI=n.
The specific value used here depends on the size of physical RAM,
how much additional virtual memory will be mapped at runtime, and
how many memory domains need to be initialized.
The current suite of Zephyr test cases may initialize at most two
additional memory domains besides the default domain.
Unused pages in this pool cannot be used for other purposes.
config X86_NO_MELTDOWN
bool