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amd64: flush L1 data cache on syscall return with an error.

Description

amd64: flush L1 data cache on syscall return with an error.

The knob allows to select the flushing mode or turn it off/on. The
idea, as well as the list of the ignored syscall errors, were taken
from https://www.openwall.com/lists/kernel-hardening/2018/10/11/10 .

I was not able to measure statistically significant difference between
flush enabled vs disabled using syscall_timing getuid.

Reviewed by: bwidawsk
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D17536

Details

Provenance
kibAuthored on Oct 20 2018, 11:17 PM
Parents
rG074244628b8c: Reduce code duplication in merging vm_entry neighbors.
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