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Groups > linux.kernel > #1363693

[PATCH v3 2/7] x86/mm/pat: Add pat_disable() interface

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In preparation for fixing a regression caused by 'commit 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 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 pat_disable() called from pat_bsp_init() to
set PAT table properly when CPU does not support PAT.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Robert Elliott <elliott@hpe.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 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 1da55a5..3c08a27 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)

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[PATCH v3 0/7] Enhance PAT init to fix Xorg crashes Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 21:50 +0100
  [PATCH v3 1/7] x86/mm/pat: Add support of non-default PAT MSR setting Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 21:50 +0100
    [tip:x86/mm] x86/mm/pat: Add support of non-default PAT MSR setting tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:40 +0200
  [PATCH v3 5/7] x86/mtrr: Fix PAT init handling when MTRR is disabled Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/mtrr: Fix PAT init handling when MTRR is disabled tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  [PATCH v3 6/7] x86/xen,pat: Remove PAT table init code from Xen Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/xen, pat: Remove PAT table init code from Xen tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  [PATCH v3 3/7] x86/mm/pat: Replace cpu_has_pat with boot_cpu_has Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/mm/pat: Replace cpu_has_pat with boot_cpu_has() tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  [PATCH v3 2/7] x86/mm/pat: Add pat_disable() interface Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/mm/pat: Add pat_disable() interface tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  [PATCH v3 7/7] x86/pat: Document PAT initialization Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/pat: Document the PAT initialization sequence tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  [PATCH v3 4/6] x86/mtrr: Fix Xorg crashes in Qemu sessions Toshi Kani <toshi.kani@hpe.com> - 2016-03-23 22:00 +0100
    [tip:x86/mm] x86/mtrr: Fix Xorg crashes in Qemu sessions tip-bot for Toshi Kani <tipbot@zytor.com> - 2016-03-29 12:50 +0200
  Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes Ingo Molnar <mingo@kernel.org> - 2016-03-29 12:40 +0200
    Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes Toshi Kani <toshi.kani@hpe.com> - 2016-03-29 15:30 +0200
      Re: [Xen-devel] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-03-29 16:50 +0200
        Re: [Xen-devel] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes Toshi Kani <toshi.kani@hpe.com> - 2016-03-29 17:00 +0200
          Re: [Xen-devel] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes "Luis R. Rodriguez" <mcgrof@suse.com> - 2016-03-30 20:10 +0200
            Re: [LKP] [Xen-devel] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes "Luis R. Rodriguez" <mcgrof@suse.com> - 2016-03-30 22:20 +0200
              Re: [LKP] [Xen-devel] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes "Luis R. Rodriguez" <mcgrof@suse.com> - 2016-03-30 22:50 +0200

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