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[ Upstream commit85c7a0f1ef] In removing the pagetable-wide lock, we gained the possibility of the vanishingly unlikely case where we have a race between two concurrent unmappers splitting the same block entry. The logic to handle this is fairly straightforward - whoever loses the race frees their partial next-level table and instead dereferences the winner's newly-installed entry in order to fall back to a regular unmap, which intentionally echoes the pre-existing case of recursively splitting a 1GB block down to 4KB pages by installing a full table of 2MB blocks first. Unfortunately, the chump who implemented that logic failed to update the condition check for that fallback, meaning that if said race occurs at the last level (where the loser's unmap_idx is valid) then the unmap won't actually happen. Fix that to properly account for both the race and recursive cases. Fixes:2c3d273eab("iommu/io-pgtable-arm: Support lockless operation") Signed-off-by: Robin Murphy <robin.murphy@arm.com> [will: re-jig control flow to avoid duplicate cmpxchg test] Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.