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Date: Tue, 4 Jul 2017 15:41:10 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Mikulas Patocka <mpatocka@...hat.com>
cc: Ingo Molnar <mingo@...nel.org>, 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>,
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: [PATCH v2] X86: don't report PAT on CPUs that don't support it
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@...hat.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@...hat.com>
Cc: Bernhard Held <berny156@....de>
Cc: Toshi Kani <toshi.kani@...com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: "Luis R. Rodriguez" <mcgrof@...e.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-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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