[tip:x86/mm] x86/mm/pat: Add pat_disable() interface

[tip-bot for Toshi Kani]

Commit-ID:  224bb1e5d67ba0f2872c98002d6a6f991ac6fd4a
Gitweb:     http://git.kernel.org/tip/224bb1e5d67ba0f2872c98002d6a6f991ac6fd4a
Author:     Toshi Kani <toshi.kani@xxxxxxx>
AuthorDate: Wed, 23 Mar 2016 15:41:58 -0600
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 29 Mar 2016 12:23:25 +0200

x86/mm/pat: Add pat_disable() interface

In preparation for fixing a regression caused by:

  9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")

... PAT needs to provide an interface that prevents the OS from
initializing the PAT MSR.

PAT MSR initialization must be done on all CPUs using the specific
sequence of operations defined in the Intel SDM.  This requires MTRRs
to be enabled since pat_init() is called as part of MTRR init
from mtrr_rendezvous_handler().

Make pat_disable() as the interface that prevents the OS from
initializing the PAT MSR.  MTRR will call this interface when it
cannot provide the SDM-defined sequence to initialize PAT.

This also assures that pat_disable() called from pat_bsp_init()
will set the PAT table properly when CPU does not support PAT.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Robert Elliott <elliott@xxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxx>
Cc: konrad.wilk@xxxxxxxxxx
Cc: paul.gortmaker@xxxxxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1458769323-24491-3-git-send-email-toshi.kani@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/pat.h |  1 +
 arch/x86/mm/pat.c          | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index 97ea55b..0ad356c 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -5,6 +5,7 @@
 #include <asm/pgtable_types.h>
 
 bool pat_enabled(void);
+void pat_disable(const char *reason);
 extern void pat_init(void);
 void __init_cache_modes(u64);
 
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index b4663885..1cc1d37 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -40,11 +40,22 @@
 static bool boot_cpu_done;
 
 static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
+static void init_cache_modes(void);
 
-static inline void pat_disable(const char *reason)
+void pat_disable(const char *reason)
 {
+	if (!__pat_enabled)
+		return;
+
+	if (boot_cpu_done) {
+		WARN_ONCE(1, "x86/PAT: PAT cannot be disabled after initialization\n");
+		return;
+	}
+
 	__pat_enabled = 0;
 	pr_info("x86/PAT: %s\n", reason);
+
+	init_cache_modes();
 }
 
 static int __init nopat(char *str)