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[ Upstream commit a2c0b0fbe0 ]
The alternatives code must be `noinstr` such that it does not patch itself,
as the cache invalidation is only performed after all the alternatives have
been applied.
Mark patch_alternative() as `noinstr`. Mark branch_insn_requires_update()
and get_alt_insn() with `__always_inline` since they are both only called
through patch_alternative().
Booting a kernel in QEMU TCG with KCSAN=y and ARM64_USE_LSE_ATOMICS=y caused
a boot hang:
[ 0.241121] CPU: All CPU(s) started at EL2
The alternatives code was patching the atomics in __tsan_read4() from LL/SC
atomics to LSE atomics.
The following fragment is using LL/SC atomics in the .text section:
| <__tsan_unaligned_read4+304>: ldxr x6, [x2]
| <__tsan_unaligned_read4+308>: add x6, x6, x5
| <__tsan_unaligned_read4+312>: stxr w7, x6, [x2]
| <__tsan_unaligned_read4+316>: cbnz w7, <__tsan_unaligned_read4+304>
This LL/SC atomic sequence was to be replaced with LSE atomics. However since
the alternatives code was instrumentable, __tsan_read4() was being called after
only the first instruction was replaced, which led to the following code in memory:
| <__tsan_unaligned_read4+304>: ldadd x5, x6, [x2]
| <__tsan_unaligned_read4+308>: add x6, x6, x5
| <__tsan_unaligned_read4+312>: stxr w7, x6, [x2]
| <__tsan_unaligned_read4+316>: cbnz w7, <__tsan_unaligned_read4+304>
This caused an infinite loop as the `stxr` instruction never completed successfully,
so `w7` was always 0.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220405104733.11476-1-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
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.
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.