linux-kernel - RE: [PATCH 3/6] x86: Add support for the clwb instruction

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Date:	Wed, 12 Nov 2014 13:38:45 +0000
From:	"Anvin, H Peter" <h.peter.anvin@...el.com>
To:	Borislav Petkov <bp@...en8.de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Airlie <airlied@...ux.ie>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH 3/6] x86: Add support for the clwb instruction

No, it doesn't.  x86 requires 3.4+ at a minimum.

________________________________
From: Borislav Petkov
Sent: Wednesday, November 12, 2014 4:39:09 AM
To: Ross Zwisler
Cc: linux-kernel@...r.kernel.org; Anvin, H Peter; Ingo Molnar; Thomas Gleixner; David Airlie; dri-devel@...ts.freedesktop.org; x86@...nel.org
Subject: Re: [PATCH 3/6] x86: Add support for the clwb instruction

On Tue, Nov 11, 2014 at 11:43:13AM -0700, Ross Zwisler wrote:
> +static inline void clwb(volatile void *__p)
> +{
> +     alternative_io_2(".byte " __stringify(NOP_DS_PREFIX) "; clflush %P0",
> +                      ".byte 0x66; clflush %P0",
> +                      X86_FEATURE_CLFLUSHOPT,
> +                      ".byte 0x66; xsaveopt %P0",

Btw, I'm afraid you're going to have to spell out those new instruction
mnemonics as they aren't supported by older compilers:

  CC      drivers/gpu/drm/drm_cache.o
{standard input}: Assembler messages:
{standard input}:63: Error: no such instruction: `xsaveopt (%rax)'
{standard input}:249: Error: no such instruction: `xsaveopt (%rdi)'
{standard input}:283: Error: no such instruction: `xsaveopt -1(%rdx)'
make[1]: *** [drivers/gpu/drm/drm_cache.o] Error 1
make: *** [drivers/gpu/drm/drm_cache.o] Error 2
[boris@...h:14:35:40:k:14)->  gcc --version
gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)

This is on a very old guest I have which has this gcc in it and the
kernel supports everything gcc >= 3.2.

--
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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