arm64: mm: Permit contiguous attribute for preliminary mappings

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There are a few cases where we omit the contiguous hint for mappings
that start out as read-write and are remapped read-only later, on the
basis that manipulating live descriptors with the PTE_CONT attribute set
is unsafe. When support for the contiguous hint was added to the code,
the ARM ARM was ambiguous about this, and so we erred on the side of
caution.

In the meantime, this has been clarified [0], and regions that will be
remapped in their entirety, retaining the contiguous bit on all entries,
can use the contiguous hint both in the initial mapping as well as the
one that replaces it. Note that this requires that the logic that may be
called to remap overlapping regions respects existing valid descriptors
that have the contiguous bit cleared.

So omit the NO_CONT_MAPPINGS flag in places where it is unneeded.

[0] RJQQTC

For a TLB lookup in a contiguous region mapped by translation table entries that
have consistent values for the Contiguous bit, but have the OA, attributes, or
permissions misprogrammed, that TLB lookup is permitted to produce an OA, access
permissions, and memory attributes that are consistent with any one of the
programmed translation table values.

Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

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Ard Biesheuvel 2026-05-29 17:01:59 +02:00 • committed by Will Deacon

parent dfd73e574d

commit 28becb2c1d

1 changed files with 3 additions and 7 deletions

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arch/arm64/mm/mmu.c

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