[Cluster-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

Luck, Tony tony.luck at intel.com
Mon Aug 30 15:41:45 UTC 2021

>> No #MC on stores. Just on loads. Note that you can't clear poison
>> state with a series of small writes to the cache line. But a single
>> 64-byte store might do it (architects didn't want to guarantee that
>> it would work when I asked about avx512 stores to clear poison
>> many years ago).
> Dave Jiang thinks MOVDIR64B clears poison.
> http://archive.lwn.net:8080/linux-kernel/157617505636.42350.1170110675242558018.stgit@djiang5-desk3.ch.intel.com/

MOVDIR64B has some explicit guarantees (does a write-back invalidate if the target is already
in the cache) that a 64-byte avx512 write doesn't.

Of course it would stop working if some future CPU were to have a longer than 64 bytes cache line.


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