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 <mpato...@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 <mpato...@redhat.com>
Cc: Bernhard Held <berny...@gmx.de>
Cc: Toshi Kani <toshi.k...@hp.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Brian Gerst <brge...@gmail.com>
Cc: "Luis R. Rodriguez" <mcg...@suse.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Denys Vlasenko <dvlas...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: sta...@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)) ||
