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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 11 Mar 2016 12:28:24 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	Borislav Petkov <bp@...en8.de>
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, 2016-03-11 at 16:54 +0100, Borislav Petkov wrote:
> 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.

Sorry, I meant to say -- "How about renaming pat_disable_init() to
pat_disable_setup()?" since I thought you had suggested to rename
pat_disable_init() to pat_setup().  I am still in favor of having a
separate setup func for the disabled case.

> > 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;

Hmm...  I do not think I understand this.  When pat_bsp_init() calls
pat_disable(), 'pat' has been set to the "Full PAT support" setup.  So, we
need to reset 'pat' to the "No PAT" setup.  How is this handled in your
case?


> >  - 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.

I think this leads more complication in the end.  pat_init() covers (too)
many scenarios already, and moving the disabled setup case out will
simplify it, IMHO.

Thanks,
-Toshi