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Re: [PATCH v2] X86: don't report PAT on CPUs that don't support it

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  Re: [PATCH v2] X86: don't report PAT on CPUs that don't support it Mikulas Patocka <mpatocka@redhat.com> - 2017-07-03 07:10 +0200
    Re: [PATCH v2] X86: don't report PAT on CPUs that don't support it Thomas Gleixner <tglx@linutronix.de> - 2017-07-04 15:50 +0200
    Re: [PATCH v2] X86: don't report PAT on CPUs that don't support it Thomas Gleixner <tglx@linutronix.de> - 2017-07-04 15:50 +0200
      [PATCH v3] X86: don't report PAT on CPUs that don't support it Mikulas Patocka <mpatocka@redhat.com> - 2017-07-05 01:10 +0200
        [tip:x86/urgent] x86/mm/pat: Don't report PAT on CPUs that don't  support it tip-bot for Mikulas Patocka <tipbot@zytor.com> - 2017-07-05 09:20 +0200

#1679643 — Re: [PATCH v2] X86: don't report PAT on CPUs that don't support it

On Tue, 6 Jun 2017, Mikulas Patocka wrote:

> Hi
> 
> Here I send the second version of the patch. It drops the change from 
> boot_cpu_has(X86_FEATURE_PAT) to this_cpu_has(X86_FEATURE_PAT) (that 
> caused kernel to be unbootable for some people).
> 
> Another change is that setup_arch() calls init_cache_modes() if PAT is 
> disabled, so that init_cache_modes() is always called.
> 
> Mikulas

Is there any progress with this patch? Will you accept it or do you want 
some changes to it?

> From: Mikulas Patocka <mpatocka@redhat.com>
> 
> In the file arch/x86/mm/pat.c, there's a variable __pat_enabled. The
> variable is set to 1 by default and the function pat_init() sets
> __pat_enabled to 0 if the CPU doesn't support PAT.
> 
> However, on AMD K6-3 CPU, the processor initialization code never calls
> pat_init() and so __pat_enabled stays 1 and the function pat_enabled()
> returns true, even though the K6-3 CPU doesn't support PAT.
> 
> The result of this bug is that this warning is produced when attemting to
> start the Xserver and the Xserver doesn't start (fork() returns ENOMEM).
> Another symptom of this bug is that the framebuffer driver doesn't set the
> K6-3 MTRR registers.
> 
> This patch changes pat_enabled() so that it returns true only if pat
> initialization was actually done.
> 
> As Andy Lutomirski suggested, we also need to call init_cache_modes() if
> pat was not initialized, so we call it after mtrr_bp_init()
> (mtrr_bp_init() would or wouldn't call pat_init()). Note that
> init_cache_modes() detects if it was called more than once and does
> nothing in that case.
> 
> x86/PAT: Xorg:3891 map pfn expected mapping type uncached-minus for [mem 0xe4000000-0xe5ffffff], got write-combining
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 3891 at arch/x86/mm/pat.c:1020 untrack_pfn+0x5c/0x9f
> Modules linked in: blowfish_generic blowfish_common cbc dm_crypt dm_loop msr configfs cpufreq_userspace cpufreq_powersave cpufreq_ondemand cpufreq_conservative ext4 crc16 jbd2 mbcache hpfs nls_cp852 msdos fat matroxfb_base matroxfb_g450 matroxfb_accel cfbfillrect cfbimgblt cfbcopyarea matroxfb_DAC1064 g450_pll matroxfb_misc floppy snd_usb_audio snd_hwdep snd_usbmidi_lib snd_seq_midi snd_seq_midi_event snd_rawmidi snd_pcm snd_seq snd_seq_device snd_timer hid_generic snd usbhid hid soundcore powernow_k6 pcspkr evdev e1000 ehci_pci uhci_hcd ehci_hcd usbcore usb_common dm_mod pata_it821x unix
> CPU: 0 PID: 3891 Comm: Xorg Not tainted 4.11.0-rc6-test+ #35
> Hardware name: System Manufacturer Product Name/VA-503A, BIOS 4.51 PG 08/02/00
> Call Trace:
>  ? __warn+0xab/0xc0
>  ? untrack_pfn+0x5c/0x9f
>  ? warn_slowpath_null+0xf/0x13
>  ? untrack_pfn+0x5c/0x9f
>  ? unmap_single_vma+0x43/0x66
>  ? unmap_vmas+0x24/0x30
>  ? exit_mmap+0x3c/0xa5
>  ? __mmput+0xf/0x76
>  ? copy_process.part.76+0xb43/0x1129
>  ? _do_fork+0x96/0x177
>  ? do_int80_syscall_32+0x3e/0x4c
>  ? entry_INT80_32+0x2a/0x2a
> ---[ end trace 8726f9d9fa90d702 ]---
> x86/PAT: Xorg:3891 map pfn expected mapping type uncached-minus for [mem 0xe4000000-0xe5ffffff], got write-combining
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org	# v4.2+
> 
> ---
>  arch/x86/include/asm/pat.h |    1 +
>  arch/x86/kernel/setup.c    |    2 ++
>  arch/x86/mm/pat.c          |   10 ++++++----
>  3 files changed, 9 insertions(+), 4 deletions(-)
> 
> Index: linux-stable/arch/x86/mm/pat.c
> ===================================================================
> --- linux-stable.orig/arch/x86/mm/pat.c
> +++ linux-stable/arch/x86/mm/pat.c
> @@ -40,7 +40,6 @@
>  static bool boot_cpu_done;
>  
>  static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
> -static void init_cache_modes(void);
>  
>  void pat_disable(const char *reason)
>  {
> @@ -65,9 +64,11 @@ static int __init nopat(char *str)
>  }
>  early_param("nopat", nopat);
>  
> +static bool __read_mostly __pat_initialized = false;
> +
>  bool pat_enabled(void)
>  {
> -	return !!__pat_enabled;
> +	return __pat_initialized;
>  }
>  EXPORT_SYMBOL_GPL(pat_enabled);
>  
> @@ -225,6 +226,7 @@ static void pat_bsp_init(u64 pat)
>  	}
>  
>  	wrmsrl(MSR_IA32_CR_PAT, pat);
> +	__pat_initialized = true;
>  
>  	__init_cache_modes(pat);
>  }
> @@ -242,7 +244,7 @@ static void pat_ap_init(u64 pat)
>  	wrmsrl(MSR_IA32_CR_PAT, pat);
>  }
>  
> -static void init_cache_modes(void)
> +void init_cache_modes(void)
>  {
>  	u64 pat = 0;
>  	static int init_cm_done;
> @@ -306,7 +308,7 @@ void pat_init(void)
>  	u64 pat;
>  	struct cpuinfo_x86 *c = &boot_cpu_data;
>  
> -	if (!pat_enabled()) {
> +	if (!__pat_enabled) {
>  		init_cache_modes();
>  		return;
>  	}
> Index: linux-stable/arch/x86/include/asm/pat.h
> ===================================================================
> --- linux-stable.orig/arch/x86/include/asm/pat.h
> +++ linux-stable/arch/x86/include/asm/pat.h
> @@ -7,6 +7,7 @@
>  bool pat_enabled(void);
>  void pat_disable(const char *reason);
>  extern void pat_init(void);
> +extern void init_cache_modes(void);
>  
>  extern int reserve_memtype(u64 start, u64 end,
>  		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
> Index: linux-stable/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-stable.orig/arch/x86/kernel/setup.c
> +++ linux-stable/arch/x86/kernel/setup.c
> @@ -1070,6 +1070,8 @@ void __init setup_arch(char **cmdline_p)
>  
>  	/* update e820 for memory not covered by WB MTRRs */
>  	mtrr_bp_init();
> +	if (!pat_enabled())
> +		init_cache_modes();
>  	if (mtrr_trim_uncached_memory(max_pfn))
>  		max_pfn = e820__end_of_ram_pfn();
>  
> 

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#1680984

On Tue, 4 Jul 2017, Thomas Gleixner wrote:
>  	wrmsrl(MSR_IA32_CR_PAT, pat);
> +	__pat_initialized = true;

That should be

> +	pat_initialized = true;

of course.

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#1680985

On Mon, 3 Jul 2017, Mikulas Patocka wrote:
> Is there any progress with this patch? Will you accept it or do you want 
> some changes to it?

Aside of the unparseable changelog, that patch is mostly duct tape.

1) __pat_enabled should be renamed to pat_disabled, as that is the actual
   purpose of that variable

2) Making the call to init_cache_modes() conditional in setup_arch() is
   pointless. init_cache_modes() has it's own protection against multiple
   invocations.

3) It adds yet another invocation of init_cache_modes() instead of getting
   rid of the ones in pat_disable() and the pat disabled case in pat_init().

I've reworked the whole thing into the patch below.

Thanks,

	tglx

8<---------------------
Subject: x86/mm/pat: Don't report PAT on CPUs that don't support it
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 6 Jun 2017 18:49:39 -0400 (EDT)

The pat_enabled() logic is broken on CPUs which do not support PAT and
where the initialization code fails to call pat_init(). Due to that the
enabled flag stays true and pat_enabled() returns true wrongfully.

As a consequence the mappings, e.g. for Xorg, are set up with the wrong
caching mode and the required MTRR setups are omitted.

To cure this the following changes are required:

  1) Make pat_enabled() return true only if PAT initialization was
     invoked and successful.

  2) Invoke init_cache_modes() unconditionally in setup_arch() and
     remove the extra callsites in pat_disable() and the pat disabled
     code path in pat_init().

Also rename __pat_enabled to pat_disabled to reflect the real purpose of
this variable.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Bernhard Held <berny156@gmx.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>

---
 arch/x86/include/asm/pat.h |    1 +
 arch/x86/kernel/setup.c    |    7 +++++++
 arch/x86/mm/pat.c          |   22 +++++++++-------------
 3 files changed, 17 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -7,6 +7,7 @@
 bool pat_enabled(void);
 void pat_disable(const char *reason);
 extern void pat_init(void);
+extern void init_cache_modes(void);
 
 extern int reserve_memtype(u64 start, u64 end,
 		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1076,6 +1076,13 @@ void __init setup_arch(char **cmdline_p)
 	max_possible_pfn = max_pfn;
 
 	/*
+	 * This call is required when the CPU does not support PAT. If
+	 * mtrr_bp_init() invoked it already via pat_init() the call has no
+	 * effect.
+	 */
+	init_cache_modes();
+
+	/*
 	 * Define random base addresses for memory sections after max_pfn is
 	 * defined and before each memory section base is used.
 	 */
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -37,14 +37,13 @@
 #undef pr_fmt
 #define pr_fmt(fmt) "" fmt
 
-static bool boot_cpu_done;
-
-static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
-static void init_cache_modes(void);
+static bool __read_mostly boot_cpu_done;
+static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
+static bool __read_mostly pat_initialized;
 
 void pat_disable(const char *reason)
 {
-	if (!__pat_enabled)
+	if (pat_disabled)
 		return;
 
 	if (boot_cpu_done) {
@@ -52,10 +51,8 @@ void pat_disable(const char *reason)
 		return;
 	}
 
-	__pat_enabled = 0;
+	pat_disabled = true;
 	pr_info("x86/PAT: %s\n", reason);
-
-	init_cache_modes();
 }
 
 static int __init nopat(char *str)
@@ -67,7 +64,7 @@ early_param("nopat", nopat);
 
 bool pat_enabled(void)
 {
-	return !!__pat_enabled;
+	return pat_initialized;
 }
 EXPORT_SYMBOL_GPL(pat_enabled);
 
@@ -225,6 +222,7 @@ static void pat_bsp_init(u64 pat)
 	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
+	__pat_initialized = true;
 
 	__init_cache_modes(pat);
 }
@@ -242,7 +240,7 @@ static void pat_ap_init(u64 pat)
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 }
 
-static void init_cache_modes(void)
+void init_cache_modes(void)
 {
 	u64 pat = 0;
 	static int init_cm_done;
@@ -306,10 +304,8 @@ void pat_init(void)
 	u64 pat;
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 
-	if (!pat_enabled()) {
-		init_cache_modes();
+	if (pat_disabled)
 		return;
-	}
 
 	if ((c->x86_vendor == X86_VENDOR_INTEL) &&
 	    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||

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#1681209 — [PATCH v3] X86: don't report PAT on CPUs that don't support it

On Tue, 4 Jul 2017, Thomas Gleixner wrote:

> On Mon, 3 Jul 2017, Mikulas Patocka wrote:
> > Is there any progress with this patch? Will you accept it or do you want 
> > some changes to it?
> 
> Aside of the unparseable changelog, that patch is mostly duct tape.
> 
> 1) __pat_enabled should be renamed to pat_disabled, as that is the actual
>    purpose of that variable
> 
> 2) Making the call to init_cache_modes() conditional in setup_arch() is
>    pointless. init_cache_modes() has it's own protection against multiple
>    invocations.
> 
> 3) It adds yet another invocation of init_cache_modes() instead of getting
>    rid of the ones in pat_disable() and the pat disabled case in pat_init().
> 
> I've reworked the whole thing into the patch below.
> 
> Thanks,
> 
> 	tglx

Yes - renaming __pat_enabled to pat_disabled is a good thing.

Just one more change - init_cache_modes() is protected against multiple 
calls, but pat_bsp_init() calls __init_cache_modes() (not 
init_cacha_modes()). The generic code would call init_cache_modes() later 
and init_cache_modes() would do the initialization again - it would be 
mostly harmless because it would just read the pat MSR that pat_bsp_init 
have written and call __init_cache_modes() with the same value - the 
symptom is that on machines with PAT we see this line twice in the syslog:

[    0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT
[    0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT

I fixed this double initialization by moving the variable init_cm_done to 
file scope and setting it in __init_cache_modes().

Mikulas


8<---------------------
Subject: x86/mm/pat: Don't report PAT on CPUs that don't support it
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 6 Jun 2017 18:49:39 -0400 (EDT)

The pat_enabled() logic is broken on CPUs which do not support PAT and
where the initialization code fails to call pat_init(). Due to that the
enabled flag stays true and pat_enabled() returns true wrongfully.

As a consequence the mappings, e.g. for Xorg, are set up with the wrong
caching mode and the required MTRR setups are omitted.

To cure this the following changes are required:

  1) Make pat_enabled() return true only if PAT initialization was
     invoked and successful.

  2) Invoke init_cache_modes() unconditionally in setup_arch() and
     remove the extra callsites in pat_disable() and the pat disabled
     code path in pat_init().

Also rename __pat_enabled to pat_disabled to reflect the real purpose of
this variable.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Bernhard Held <berny156@gmx.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org	# v4.2+

---
 arch/x86/include/asm/pat.h |    1 +
 arch/x86/kernel/setup.c    |    7 +++++++
 arch/x86/mm/pat.c          |   28 ++++++++++++----------------
 3 files changed, 20 insertions(+), 16 deletions(-)

Index: linux-2.6/arch/x86/include/asm/pat.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/pat.h
+++ linux-2.6/arch/x86/include/asm/pat.h
@@ -7,6 +7,7 @@
 bool pat_enabled(void);
 void pat_disable(const char *reason);
 extern void pat_init(void);
+extern void init_cache_modes(void);
 
 extern int reserve_memtype(u64 start, u64 end,
 		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
Index: linux-2.6/arch/x86/kernel/setup.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/setup.c
+++ linux-2.6/arch/x86/kernel/setup.c
@@ -1076,6 +1076,13 @@ void __init setup_arch(char **cmdline_p)
 	max_possible_pfn = max_pfn;
 
 	/*
+	 * This call is required when the CPU does not support PAT. If
+	 * mtrr_bp_init() invoked it already via pat_init() the call has no
+	 * effect.
+	 */
+	init_cache_modes();
+
+	/*
 	 * Define random base addresses for memory sections after max_pfn is
 	 * defined and before each memory section base is used.
 	 */
Index: linux-2.6/arch/x86/mm/pat.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/pat.c
+++ linux-2.6/arch/x86/mm/pat.c
@@ -37,14 +37,14 @@
 #undef pr_fmt
 #define pr_fmt(fmt) "" fmt
 
-static bool boot_cpu_done;
-
-static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
-static void init_cache_modes(void);
+static bool __read_mostly boot_cpu_done;
+static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
+static bool __read_mostly pat_initialized;
+static bool __read_mostly init_cm_done;
 
 void pat_disable(const char *reason)
 {
-	if (!__pat_enabled)
+	if (pat_disabled)
 		return;
 
 	if (boot_cpu_done) {
@@ -52,10 +52,8 @@ void pat_disable(const char *reason)
 		return;
 	}
 
-	__pat_enabled = 0;
+	pat_disabled = true;
 	pr_info("x86/PAT: %s\n", reason);
-
-	init_cache_modes();
 }
 
 static int __init nopat(char *str)
@@ -67,7 +65,7 @@ early_param("nopat", nopat);
 
 bool pat_enabled(void)
 {
-	return !!__pat_enabled;
+	return pat_initialized;
 }
 EXPORT_SYMBOL_GPL(pat_enabled);
 
@@ -205,6 +203,8 @@ static void __init_cache_modes(u64 pat)
 		update_cache_mode_entry(i, cache);
 	}
 	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
+
+	init_cm_done = true;
 }
 
 #define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
@@ -225,6 +225,7 @@ static void pat_bsp_init(u64 pat)
 	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
+	pat_initialized = true;
 
 	__init_cache_modes(pat);
 }
@@ -242,10 +243,9 @@ static void pat_ap_init(u64 pat)
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 }
 
-static void init_cache_modes(void)
+void init_cache_modes(void)
 {
 	u64 pat = 0;
-	static int init_cm_done;
 
 	if (init_cm_done)
 		return;
@@ -287,8 +287,6 @@ static void init_cache_modes(void)
 	}
 
 	__init_cache_modes(pat);
-
-	init_cm_done = 1;
 }
 
 /**
@@ -306,10 +304,8 @@ void pat_init(void)
 	u64 pat;
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 
-	if (!pat_enabled()) {
-		init_cache_modes();
+	if (pat_disabled)
 		return;
-	}
 
 	if ((c->x86_vendor == X86_VENDOR_INTEL) &&
 	    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||

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#1681331 — [tip:x86/urgent] x86/mm/pat: Don't report PAT on CPUs that don't support it

Commit-ID:  99c13b8c8896d7bcb92753bf0c63a8de4326e78d
Gitweb:     http://git.kernel.org/tip/99c13b8c8896d7bcb92753bf0c63a8de4326e78d
Author:     Mikulas Patocka <mpatocka@redhat.com>
AuthorDate: Tue, 4 Jul 2017 19:04:23 -0400
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 5 Jul 2017 09:01:24 +0200

x86/mm/pat: Don't report PAT on CPUs that don't support it

The pat_enabled() logic is broken on CPUs which do not support PAT and
where the initialization code fails to call pat_init(). Due to that the
enabled flag stays true and pat_enabled() returns true wrongfully.

As a consequence the mappings, e.g. for Xorg, are set up with the wrong
caching mode and the required MTRR setups are omitted.

To cure this the following changes are required:

  1) Make pat_enabled() return true only if PAT initialization was
     invoked and successful.

  2) Invoke init_cache_modes() unconditionally in setup_arch() and
     remove the extra callsites in pat_disable() and the pat disabled
     code path in pat_init().

Also rename __pat_enabled to pat_disabled to reflect the real purpose of
this variable.

Fixes: 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Bernhard Held <berny156@gmx.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1707041749300.3456@file01.intranet.prod.int.rdu2.redhat.com

---
 arch/x86/include/asm/pat.h |  1 +
 arch/x86/kernel/setup.c    |  7 +++++++
 arch/x86/mm/pat.c          | 28 ++++++++++++----------------
 3 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index 0b1ff4c..fffb279 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -7,6 +7,7 @@
 bool pat_enabled(void);
 void pat_disable(const char *reason);
 extern void pat_init(void);
+extern void init_cache_modes(void);
 
 extern int reserve_memtype(u64 start, u64 end,
 		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 65622f0..3486d04 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1076,6 +1076,13 @@ void __init setup_arch(char **cmdline_p)
 	max_possible_pfn = max_pfn;
 
 	/*
+	 * This call is required when the CPU does not support PAT. If
+	 * mtrr_bp_init() invoked it already via pat_init() the call has no
+	 * effect.
+	 */
+	init_cache_modes();
+
+	/*
 	 * Define random base addresses for memory sections after max_pfn is
 	 * defined and before each memory section base is used.
 	 */
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 9b78685..4597950 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -37,14 +37,14 @@
 #undef pr_fmt
 #define pr_fmt(fmt) "" fmt
 
-static bool boot_cpu_done;
-
-static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
-static void init_cache_modes(void);
+static bool __read_mostly boot_cpu_done;
+static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
+static bool __read_mostly pat_initialized;
+static bool __read_mostly init_cm_done;
 
 void pat_disable(const char *reason)
 {
-	if (!__pat_enabled)
+	if (pat_disabled)
 		return;
 
 	if (boot_cpu_done) {
@@ -52,10 +52,8 @@ void pat_disable(const char *reason)
 		return;
 	}
 
-	__pat_enabled = 0;
+	pat_disabled = true;
 	pr_info("x86/PAT: %s\n", reason);
-
-	init_cache_modes();
 }
 
 static int __init nopat(char *str)
@@ -67,7 +65,7 @@ early_param("nopat", nopat);
 
 bool pat_enabled(void)
 {
-	return !!__pat_enabled;
+	return pat_initialized;
 }
 EXPORT_SYMBOL_GPL(pat_enabled);
 
@@ -205,6 +203,8 @@ static void __init_cache_modes(u64 pat)
 		update_cache_mode_entry(i, cache);
 	}
 	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
+
+	init_cm_done = true;
 }
 
 #define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
@@ -225,6 +225,7 @@ static void pat_bsp_init(u64 pat)
 	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
+	pat_initialized = true;
 
 	__init_cache_modes(pat);
 }
@@ -242,10 +243,9 @@ static void pat_ap_init(u64 pat)
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 }
 
-static void init_cache_modes(void)
+void init_cache_modes(void)
 {
 	u64 pat = 0;
-	static int init_cm_done;
 
 	if (init_cm_done)
 		return;
@@ -287,8 +287,6 @@ static void init_cache_modes(void)
 	}
 
 	__init_cache_modes(pat);
-
-	init_cm_done = 1;
 }
 
 /**
@@ -306,10 +304,8 @@ void pat_init(void)
 	u64 pat;
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 
-	if (!pat_enabled()) {
-		init_cache_modes();
+	if (pat_disabled)
 		return;
-	}
 
 	if ((c->x86_vendor == X86_VENDOR_INTEL) &&
 	    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||

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