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From: Junichi Nomura <j-nomura@ce.jp.nec.com>
To: Mikulas Patocka <mpatocka@redhat.com>
CC: Dominik Brodowski <linux@dominikbrodowski.net>,
        Bernhard Held <berny156@gmx.de>, Andy Lutomirski <luto@kernel.org>,
        Toshi Kani <toshi.kani@hp.com>, Borislav Petkov <bp@alien8.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, "Ingo Molnar" <mingo@kernel.org>,
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        "Peter Zijlstra" <peterz@infradead.org>,
        "Luis R. Rodriguez" <mcgrof@suse.com>,
        "Denys Vlasenko" <dvlasenk@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [tip:x86/urgent] x86/PAT: Fix Xorg regression on CPUs that
 don't support PAT
Thread-Topic: [tip:x86/urgent] x86/PAT: Fix Xorg regression on CPUs that
 don't support PAT
Thread-Index: AQHS1+B8N4QEAx/Plk+8J3I1iJulDKIJffkAgAHXd4CAATRgAIAADJSAgAEGdYA=
Date: Wed, 31 May 2017 09:39:03 +0000
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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.