[RFC v2 PATCH 0/7] x86/entry: simplify and unify SAVE/POP_REGS

Dominik Brodowski
2018-02-07T20:19:46Z

The starting point for this series was the intention to interleave
the register clearing with register PUSH or MOV instructions, in order
to minimize the cost of the additional instructions required for the
register clearing. While at it, I noticed that a couple of macros in
arch/x86/entry/calling.h are unused and can be cleaned up.

Based on a preliminary version of this patch,[*] Linus suggested to
merge further codepaths and to use PUSH instead of MOV, as this should
be faster on newer CPUs.

[*] http://lkml.kernel.org/r/20180206212546.GA2026@light.dominikbrodowski.net and
http://lkml.kernel.org/r/20180206213202.GB2026@light.dominikbrodowski.net

NOTE / WARNING: Please be *extremely* stringent in reviewing these
patches, *especially* concerning patch 6/7 (x86/entry: get rid of
ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS).

Dominik Brodowski (7):
x86/entry: merge SAVE_C_REGS and SAVE_EXTRA_REGS, remove unused
extensions
x86/entry: merge POP_C_REGS and POP_EXTRA_REGS
x86/entry: interleave XOR register clearing with PUSH instructions
x86/entry: introduce PUSH_AND_CLEAN_REGS
x86/entry: use PUSH_AND_CLEAN_REGS in more cases
x86/entry: get rid of ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS
x86/entry: indent PUSH_AND_CLEAR_REGS and POP_REGS properly

arch/x86/entry/calling.h | 118 ++++++++++++++++++----------------------------
arch/x86/entry/entry_64.S | 104 +++++++---------------------------------
2 files changed, 62 insertions(+), 160 deletions(-)

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2.16.1