ARM: fix hash_name() and branch predictor issues
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- v1 Latest0 of 3 patches 11 repliesIn review
Patches in v1 No applies recorded yet
None of the 3 patches the cover letter announces are in this archive.
Reviews trailers per patch
| Patch | Xie Yuanbin |
|---|---|
| Series | R-b T-b R-b T-b T-b |
Trailers given in replies are filled; those carried in the patches from earlier versions are outlined with dashes.
Cover letter [PATCH 0/3] ARM: fix hash_name() and branch predictor issues
This series, which I'm intending to be part of my upcoming pull request for this merge window (note - will be sent before Thursday, otherwise it won't be until maybe the middle of January) fixes the recently reported hash_name() issue, and also the long standing branch predictor hardening smp_processor_id() warning which occurs due to interrupts being enabled.
Fixing this isn't trivial because there are many paths through do_page_fault() which are non-obvious.
For example, we detect page faults by the kernel attempting to execute memory that it shouldn't and print such a warning. If we introduce an early address check, we avoid that detection, making it become a plain kernel oops without the informative error message.
The first patch adds an additional check in __do_kernel_fault() to detect this condition. This patch is a non-obvious dependency for the next patch.
The second patch handles faults above the top of userspace entirely separately, meaning we have a simpler and more obvious fault path, which avoids any possibility of taking any MM mutexes, which is the cause of the hash_name() problem.
The third patch moves harden_branch_predictor() out of __do_user_fault() and to appropriate places in the parent functions. The reason this has been avoided thus far is because do_page_fault() can be a hot path (since it's used for page aging as well) but with kernel address faults being handled by an entirely separate path, this avoids adding to that overhead.
I would like to get some attributations for this - specifically tested-by.
Thanks.
arch/arm/mm/alignment.c | 6 +++- arch/arm/mm/fault.c | 74 +++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 67 insertions(+), 13 deletions(-)
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