linux-kernel - Re: [PATCH] x86: Add an explicit barrier() to clflushopt()

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Message-ID: <20151019112526.GB20341@pd.tnic>
Date:	Mon, 19 Oct 2015 13:25:26 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	linux-kernel@...r.kernel.org,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...ux.intel.com>,
	Imre Deak <imre.deak@...el.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] x86: Add an explicit barrier() to clflushopt()

On Mon, Oct 19, 2015 at 12:05:29PM +0100, Chris Wilson wrote:
> In order to add the clobbers, I had to adjust the macro slightly:
> 
> +#define alternative_output(oldinstr, newinstr, feature, output)        \
> +       asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
> +               : output : "i" (0) : "memory")
> 
> and that also works. The concern I have here is that the asm does use
> "+m" as its output already, and the clflush() asm doesn't require the
> manual clobber.

Yeah, you could make the above

#define alternative_output(oldinstr, newinstr, feature, output, clobber...)

and use it to define clflushopt(). hpa might have a better idea, though...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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