linux-kernel - Re: [PATCH v2 16/17] x86/insn: remove pcommit

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Date:	Fri, 22 Jul 2016 08:55:23 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...e.de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v2 16/17] x86/insn: remove pcommit

On Tue, Jul 12, 2016 at 3:12 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Jul 12, 2016 at 7:57 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>> On Sat, Jul 09, 2016 at 08:25:54PM -0700, Dan Williams wrote:
>>> The pcommit instruction is being deprecated in favor of either ADR
>>> (asynchronous DRAM refresh: flush-on-power-fail) at the platform level, or
>>> posted-write-queue flush addresses as defined by the ACPI 6.x NFIT (NVDIMM
>>> Firmware Interface Table).
>>
>>>  arch/x86/include/asm/cpufeatures.h                 |    1
>>>  arch/x86/include/asm/special_insns.h               |   46 --------------------
>>>  arch/x86/lib/x86-opcode-map.txt                    |    2 -
>>>  tools/objtool/arch/x86/insn/x86-opcode-map.txt     |    2 -
>>>  tools/perf/arch/x86/tests/insn-x86-dat-32.c        |    2 -
>>>  tools/perf/arch/x86/tests/insn-x86-dat-64.c        |    2 -
>>>  tools/perf/arch/x86/tests/insn-x86-dat-src.c       |    4 --
>>
>> Just deprecated, or is it completely eradicated, removed from history,
>> will never ever happen and we'll reissue the opcode for something else?
>>
>> Because if its only deprecated then removing it from the instruction
>> decoders seems wrong, old binaries might still contain the opcode.
>
> Eradicated.
>
> "The new instructions like CLWB and CLFLUSHOPT will be rolled into the
> SDM but PCOMMIT will be removed from the Extensions doc and not rolled
> into the SDM." [1]
>
> Existing binaries are already gating their usage on the presence of
> the cpu id flag, that flag and the instruction opcode are reserved
> going forward.
>
> [1]: https://lists.01.org/pipermail/linux-nvdimm/2016-June/005923.html

x86 maintainers, I have the other patches in this series queued in
-next. Please ack this one and I'll add it for v4.8-rc1, or otherwise
let me know how you want to handle this patch.