linux-kernel - Re: [tip:x86/urgent] x86/PAT: Fix Xorg regression on CPUs that don't support PAT

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Date:   Wed, 31 May 2017 09:39:03 +0000
From:   Junichi Nomura <j-nomura@...jp.nec.com>
To:     Mikulas Patocka <mpatocka@...hat.com>
CC:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Bernhard Held <berny156@....de>,
        Andy Lutomirski <luto@...nel.org>,
        Toshi Kani <toshi.kani@...com>, Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>,
        "Denys Vlasenko" <dvlasenk@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/PAT: Fix Xorg regression on CPUs that
 don't support PAT

On 05/31/17 02:59, Mikulas Patocka wrote:
>>> 2. use the PAT patch and revert the change to the function pat_ap_init
>>> - i.e. change it to the original:
>>> static void pat_ap_init(u64 pat)
>>> {
>>> 	if (!boot_cpu_has(X86_FEATURE_PAT)) {
>>
>> Joy.
> 
> It is interesting - does it mean that the boot cpu does have PAT and the 
> secondary CPUs don't?

It seems pat_init() is called twice for boot cpu, from mtrr_bp_pat_init()
and generic_set_all(). The 2nd call ends up calling pat_ap_init() and it's
before boot_cpu_data is copied to cpu_data[0].

-- 
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.