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

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>,
	Thomas Gleixner <tglx@linutronix.de>,
	"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
Date: Wed, 31 May 2017 09:39:03 +0000	[thread overview]
Message-ID: <60179b8d-319d-8860-a599-29577fb9fe26@ce.jp.nec.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1705301353130.17960@file01.intranet.prod.int.rdu2.redhat.com>

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.