linux-kernel - Re: [PATCH 1/2] x86/mm/pat: Change pat

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Date:	Fri, 11 Mar 2016 16:54:39 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Toshi Kani <toshi.kani@....com>
Cc:	"mingo@...nel.org" <mingo@...nel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mcgrof@...e.com" <mcgrof@...e.com>,
	"jgross@...e.com" <jgross@...e.com>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/mm/pat: Change pat_disable() to emulate PAT table

On Fri, Mar 11, 2016 at 09:27:40AM -0700, Toshi Kani wrote:
> How about pat_disable_setup()?  It's only used for the disabled case, so
> I'd prefer to keep the word "disable".

What for?

Renaming pat_init() to pat_setup() is perfectly fine as it sets up PAT
after looking at pat_disabled() setting and after looking at the CPU
vendor. Sounds like a perfectly sane design to me.

> Yes, calling pat_init() from pat_disable() works too. I changed it in this
> way because:
>  - pat_bsp_init() calls pat_disabled() in an error case. It is simpler to
> avoid a recursive call to pat_init().

So do this:

static inline void pat_disable(const char *reason)
{
	if (!__pat_enabled)
		return;


>  - pat_bsp_init() has two different error paths, 1) call pat_disable() and
> return, and 2) goto done and call pat_init_cache_modes(). We can remove
> case 2) to keep the error handling consistent in this way.

Above.

> > Then you don't have to add yet another static disable_init_done but rely
> > on boot_cpu_done which gets set in pat_init().
> 
> Right, but it will do 'boot_cpu_done = true' twice, and this implicit
> recursive call may cause an issue in future if someone makes change
> carelessly.

So move boot_cpu_done into pat_bsp_init() and make it protect that
function from a being called a second time.

-- 
Regards/Gruss,
    Boris.

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