[PATCH v3 1/7] x86/mm/pat: Add support of non-default PAT MSR setting

[PATCH v3 1/7] x86/mm/pat: Add support of non-default PAT MSR setting

[Toshi Kani]

In preparation for fixing a regression caused by 'commit 9cd25aac1f44
("x86/mm/pat: Emulate PAT when it is disabled")', PAT needs to
support a case that PAT MSR is initialized with a non-default
value.

When pat_init() is called and PAT is disabled, it initializes
PAT table with the BIOS default value. Xen, however, sets PAT MSR
with a non-default value to enable WC. This causes inconsistency
between PAT table and PAT MSR when PAT is set to disable on Xen.

Change pat_init() to handle the PAT disable cases properly.  Add
init_cache_modes() to handle two cases when PAT is set to disable.
 1. CPU supports PAT: Set PAT table to be consistent with PAT MSR.
 2. CPU does not support PAT: Set PAT table to be consistent with
    PWT and PCD bits in a PTE.

Note, __init_cache_modes(), renamed from pat_init_cache_modes(),
will be changed to a static function in a later patch.

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: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/pat.h |    2 +
 arch/x86/mm/pat.c          |   73 ++++++++++++++++++++++++++++++++------------
 arch/x86/xen/enlighten.c   |    2 +
 3 files changed, 55 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index ca6c228..97ea55b 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -6,7 +6,7 @@
 
 bool pat_enabled(void);
 extern void pat_init(void);
-void pat_init_cache_modes(u64);
+void __init_cache_modes(u64);
 
 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/mm/pat.c b/arch/x86/mm/pat.c
index 04e2e71..1da55a5 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -181,7 +181,7 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
  * configuration.
  * Using lower indices is preferred, so we start with highest index.
  */
-void pat_init_cache_modes(u64 pat)
+void __init_cache_modes(u64 pat)
 {
 	enum page_cache_mode cache;
 	char pat_msg[33];
@@ -207,9 +207,6 @@ static void pat_bsp_init(u64 pat)
 		return;
 	}
 
-	if (!pat_enabled())
-		goto done;
-
 	rdmsrl(MSR_IA32_CR_PAT, tmp_pat);
 	if (!tmp_pat) {
 		pat_disable("PAT MSR is 0, disabled.");
@@ -218,15 +215,11 @@ static void pat_bsp_init(u64 pat)
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 
-done:
-	pat_init_cache_modes(pat);
+	__init_cache_modes(pat);
 }
 
 static void pat_ap_init(u64 pat)
 {
-	if (!pat_enabled())
-		return;
-
 	if (!cpu_has_pat) {
 		/*
 		 * If this happens we are on a secondary CPU, but switched to
@@ -238,18 +231,32 @@ static void pat_ap_init(u64 pat)
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 }
 
-void pat_init(void)
+static void init_cache_modes(void)
 {
-	u64 pat;
-	struct cpuinfo_x86 *c = &boot_cpu_data;
+	u64 pat = 0;
+	static int init_cm_done;
 
-	if (!pat_enabled()) {
+	if (init_cm_done)
+		return;
+
+	if (boot_cpu_has(X86_FEATURE_PAT)) {
+		/*
+		 * CPU supports PAT. Set PAT table to be consistent with
+		 * PAT MSR. This case supports "nopat" boot option, and
+		 * virtual machine environments which support PAT without
+		 * MTRRs. In specific, Xen has unique setup to PAT MSR.
+		 *
+		 * If PAT MSR returns 0, it is considered invalid and emulates
+		 * as No PAT.
+		 */
+		rdmsrl(MSR_IA32_CR_PAT, pat);
+	}
+
+	if (!pat) {
 		/*
 		 * No PAT. Emulate the PAT table that corresponds to the two
-		 * cache bits, PWT (Write Through) and PCD (Cache Disable). This
-		 * setup is the same as the BIOS default setup when the system
-		 * has PAT but the "nopat" boot option has been specified. This
-		 * emulated PAT table is used when MSR_IA32_CR_PAT returns 0.
+		 * cache bits, PWT (Write Through) and PCD (Cache Disable).
+		 * This setup is also the same as the BIOS default setup.
 		 *
 		 * PTE encoding:
 		 *
@@ -266,10 +273,36 @@ void pat_init(void)
 		 */
 		pat = PAT(0, WB) | PAT(1, WT) | PAT(2, UC_MINUS) | PAT(3, UC) |
 		      PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC);
+	}
+
+	__init_cache_modes(pat);
+
+	init_cm_done = 1;
+}
+
+/**
+ * pat_init - Initialize PAT MSR and PAT table
+ *
+ * This function initializes PAT MSR and PAT table with an OS-defined value
+ * to enable additional cache attributes, WC and WT.
+ *
+ * This function must be called on all CPUs using the specific sequence of
+ * operations defined in Intel SDM. mtrr_rendezvous_handler() provides this
+ * procedure for PAT.
+ */
+void pat_init(void)
+{
+	u64 pat;
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+
+	if (!pat_enabled()) {
+		init_cache_modes();
+		return;
+	}
 
-	} else if ((c->x86_vendor == X86_VENDOR_INTEL) &&
-		   (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||
-		    ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) {
+	if ((c->x86_vendor == X86_VENDOR_INTEL) &&
+	    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||
+	     ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) {
 		/*
 		 * PAT support with the lower four entries. Intel Pentium 2,
 		 * 3, M, and 4 are affected by PAT errata, which makes the
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2379a5a..f4296b6 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1623,7 +1623,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	 * configuration.
 	 */
 	rdmsrl(MSR_IA32_CR_PAT, pat);
-	pat_init_cache_modes(pat);
+	__init_cache_modes(pat);
 
 	/* keep using Xen gdt for now; no urgent need to change it */
 

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

[Toshi Kani]

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 3/7] x86/mm/pat: Replace cpu_has_pat with boot_cpu_has

[Toshi Kani]

Borislav Petkov wrote:
> Please use on init paths boot_cpu_has(X86_FEATURE_PAT) and on fast
> paths static_cpu_has(X86_FEATURE_PAT). No more of that cpu_has_XXX
> ugliness.

Replace the use of cpu_has_pat on init paths with boot_cpu_has().

Suggested-by: Borislav Petkov <bp@suse.de>
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/mm/pat.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 3c08a27..3aea1ab 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -213,7 +213,7 @@ static void pat_bsp_init(u64 pat)
 {
 	u64 tmp_pat;
 
-	if (!cpu_has_pat) {
+	if (!boot_cpu_has(X86_FEATURE_PAT)) {
 		pat_disable("PAT not supported by CPU.");
 		return;
 	}
@@ -231,7 +231,7 @@ static void pat_bsp_init(u64 pat)
 
 static void pat_ap_init(u64 pat)
 {
-	if (!cpu_has_pat) {
+	if (!boot_cpu_has(X86_FEATURE_PAT)) {
 		/*
 		 * If this happens we are on a secondary CPU, but switched to
 		 * PAT on the boot CPU. We have no way to undo PAT.

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[PATCH v3 4/6] x86/mtrr: Fix Xorg crashes in Qemu sessions

[Toshi Kani]

A Xorg failure on qemu32 was reported as a regression [1] caused by
'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")'.
This patch fixes this regression.

Negative effects of this regression were the following two failures [2]
in Xorg on QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were
triggered by the fact that its virtual CPU does not support MTRRs.

 #1. copy_process() failed in the check in reserve_pfn_range()

    copy_process
     copy_mm
      dup_mm
       dup_mmap
        copy_page_range
         track_pfn_copy
          reserve_pfn_range

 A WC map request was tracked as WC in memtype, which set a PTE as
 UC (pgprot) per __cachemode2pte_tbl[].  This led to this error in
 reserve_pfn_range() called from track_pfn_copy(), which obtained
 a pgprot from a PTE.  It converts pgprot to page_cache_mode, which
 does not necessarily result in the original page_cache_mode since
 __cachemode2pte_tbl[] redirects multiple types to UC.

 #2. error path in copy_process() then hit WARN_ON_ONCE in
     untrack_pfn().

     x86/PAT: Xorg:509 map pfn expected mapping type uncached-
     minus for [mem 0xfd000000-0xfdffffff], got write-combining
      Call Trace:
     dump_stack
     warn_slowpath_common
     ? untrack_pfn
     ? untrack_pfn
     warn_slowpath_null
     untrack_pfn
     ? __kunmap_atomic
     unmap_single_vma
     ? pagevec_move_tail_fn
     unmap_vmas
     exit_mmap
     mmput
     copy_process.part.47
     _do_fork
     SyS_clone
     do_syscall_32_irqs_on
     entry_INT80_32

These negative effects are caused by two separate bugs, but they
can be addressed in separate patches.  Fixing the pat_init() issue
described below addresses the root cause, and avoids Xorg to hit
these cases.

When the CPU does not support MTRRs, MTRR does not call pat_init(),
which leaves PAT enabled without initializing PAT.  This pat_init()
issue is a long-standing issue, but manifested as issue #1 (and then
hit issue #2) with the above-mentioned commit because the memtype
now tracks cache attribute with 'page_cache_mode'.

This pat_init() issue existed before the commit, but we used pgprot
in memtype.  Hence, we did not have issue #1 before.  But WC request
resulted in WT in effect because WC pgrot is actually WT when PAT
is not initialized.  This is not how it was designed to work.  When
PAT is set to disable properly, WC is converted to UC.  The use of
WT can result in a system crash if the target range does not support
WT.  Fortunately, nobody ran into such issue before.

To fix this pat_init() issue, PAT code has been enhanced to provide
pat_disable() interface.  Call this interface when MTRRs are disabled.
By setting PAT to disable properly, PAT bypasses the memtype check,
and avoids issue #1.

[1]: https://lkml.org/lkml/2016/3/3/828
[2]: https://lkml.org/lkml/2016/3/4/775
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: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/mtrr.h     |    6 +++++-
 arch/x86/kernel/cpu/mtrr/main.c |   10 +++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
index b94f6f6..dbff145 100644
--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -24,6 +24,7 @@
 #define _ASM_X86_MTRR_H
 
 #include <uapi/asm/mtrr.h>
+#include <asm/pat.h>
 
 
 /*
@@ -83,9 +84,12 @@ static inline int mtrr_trim_uncached_memory(unsigned long end_pfn)
 static inline void mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi)
 {
 }
+static inline void mtrr_bp_init(void)
+{
+	pat_disable("MTRRs disabled, skipping PAT initialization too.");
+}
 
 #define mtrr_ap_init() do {} while (0)
-#define mtrr_bp_init() do {} while (0)
 #define set_mtrr_aps_delayed_init() do {} while (0)
 #define mtrr_aps_init() do {} while (0)
 #define mtrr_bp_restore() do {} while (0)
diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 10f8d47..8b1947b 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -759,8 +759,16 @@ void __init mtrr_bp_init(void)
 		}
 	}
 
-	if (!mtrr_enabled())
+	if (!mtrr_enabled()) {
 		pr_info("MTRR: Disabled\n");
+
+		/*
+		 * PAT initialization relies on MTRR's rendezvous handler.
+		 * Skip PAT init until the handler can initialize both
+		 * features independently.
+		 */
+		pat_disable("MTRRs disabled, skipping PAT initialization too.");
+	}
 }
 
 void mtrr_ap_init(void)

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[PATCH v3 5/7] x86/mtrr: Fix PAT init handling when MTRR is disabled

[Toshi Kani]

get_mtrr_state() calls pat_init() on BSP even if MTRR is disabled.
This results in calling pat_init() on BSP only since APs do not call
pat_init() when MTRR is disabled.  This inconsistency between BSP
and APs leads to undefined behavior.

Make BSP's calling condition to pat_init() consistent with AP's,
mtrr_ap_init() and mtrr_aps_init().

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: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/mtrr/generic.c |   24 ++++++++++++++----------
 arch/x86/kernel/cpu/mtrr/main.c    |    3 +++
 arch/x86/kernel/cpu/mtrr/mtrr.h    |    1 +
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index fcbcb2f..a9d2e54 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -444,11 +444,24 @@ static void __init print_mtrr_state(void)
 		pr_debug("TOM2: %016llx aka %lldM\n", mtrr_tom2, mtrr_tom2>>20);
 }
 
+/* PAT setup for BP. We need to go through sync steps here */
+void __init mtrr_bp_pat_init(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	prepare_set();
+
+	pat_init();
+
+	post_set();
+	local_irq_restore(flags);
+}
+
 /* Grab all of the MTRR state for this CPU into *state */
 bool __init get_mtrr_state(void)
 {
 	struct mtrr_var_range *vrs;
-	unsigned long flags;
 	unsigned lo, dummy;
 	unsigned int i;
 
@@ -481,15 +494,6 @@ bool __init get_mtrr_state(void)
 
 	mtrr_state_set = 1;
 
-	/* PAT setup for BP. We need to go through sync steps here */
-	local_irq_save(flags);
-	prepare_set();
-
-	pat_init();
-
-	post_set();
-	local_irq_restore(flags);
-
 	return !!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED);
 }
 
diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 8b1947b..7d393ec 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -752,6 +752,9 @@ void __init mtrr_bp_init(void)
 			/* BIOS may override */
 			__mtrr_enabled = get_mtrr_state();
 
+			if (mtrr_enabled())
+				mtrr_bp_pat_init();
+
 			if (mtrr_cleanup(phys_addr)) {
 				changed_by_mtrr_cleanup = 1;
 				mtrr_if->set_all();
diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.h b/arch/x86/kernel/cpu/mtrr/mtrr.h
index 951884d..6c7ced0 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.h
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.h
@@ -52,6 +52,7 @@ void set_mtrr_prepare_save(struct set_mtrr_context *ctxt);
 void fill_mtrr_var_range(unsigned int index,
 		u32 base_lo, u32 base_hi, u32 mask_lo, u32 mask_hi);
 bool get_mtrr_state(void);
+void mtrr_bp_pat_init(void);
 
 extern void set_mtrr_ops(const struct mtrr_ops *ops);
 

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[PATCH v3 6/7] x86/xen, pat: Remove PAT table init code from Xen

[Toshi Kani]

Xen supports PAT without MTRRs for its guests.  In order to
enable WC attribute, it was necessary for xen_start_kernel()
to call pat_init_cache_modes() to update PAT table before
starting guest kernel.

Now that the kernel initializes PAT table to the BIOS handoff
state when MTRR is disabled, this Xen-specific PAT init code
is no longer necessary.  Delete it from xen_start_kernel().

Also change __init_cache_modes() to a static function since
PAT table should not be tweaked by other modules.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Juergen Gross <jgross@suse.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          |    2 +-
 arch/x86/xen/enlighten.c   |    9 ---------
 3 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index 0ad356c..0b1ff4c 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -7,7 +7,6 @@
 bool pat_enabled(void);
 void pat_disable(const char *reason);
 extern void pat_init(void);
-void __init_cache_modes(u64);
 
 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/mm/pat.c b/arch/x86/mm/pat.c
index 3aea1ab..9db6915 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -192,7 +192,7 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
  * configuration.
  * Using lower indices is preferred, so we start with highest index.
  */
-void __init_cache_modes(u64 pat)
+static void __init_cache_modes(u64 pat)
 {
 	enum page_cache_mode cache;
 	char pat_msg[33];
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index f4296b6..d5f172d 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -75,7 +75,6 @@
 #include <asm/mach_traps.h>
 #include <asm/mwait.h>
 #include <asm/pci_x86.h>
-#include <asm/pat.h>
 #include <asm/cpu.h>
 
 #ifdef CONFIG_ACPI
@@ -1511,7 +1510,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
 {
 	struct physdev_set_iopl set_iopl;
 	unsigned long initrd_start = 0;
-	u64 pat;
 	int rc;
 
 	if (!xen_start_info)
@@ -1618,13 +1616,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
 				   xen_start_info->nr_pages);
 	xen_reserve_special_pages();
 
-	/*
-	 * Modify the cache mode translation tables to match Xen's PAT
-	 * configuration.
-	 */
-	rdmsrl(MSR_IA32_CR_PAT, pat);
-	__init_cache_modes(pat);
-
 	/* keep using Xen gdt for now; no urgent need to change it */
 
 #ifdef CONFIG_X86_32

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[PATCH v3 7/7] x86/pat: Document PAT initialization

[Toshi Kani]

Update PAT documentation to describe how PAT is initialized under
various configurations.

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: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 Documentation/x86/pat.txt |   32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt
index 54944c7..8ccc0fc 100644
--- a/Documentation/x86/pat.txt
+++ b/Documentation/x86/pat.txt
@@ -196,3 +196,35 @@ Another, more verbose way of getting PAT related debug messages is with
 "debugpat" boot parameter. With this parameter, various debug messages are
 printed to dmesg log.
 
+PAT Initialization
+------------------
+
+The following table describes how PAT is initialized under various
+configurations. PAT MSR must be updated by Linux in order to support WC
+and WT attributes. Otherwise, the PAT MSR has the value programmed in it
+by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
+
+ MTRR PAT   Call Sequence               PAT State  PAT MSR
+ =========================================================
+ E    E     MTRR -> PAT init            Enabled    OS
+ E    D     MTRR -> PAT init            Disabled    -
+ D    E     MTRR -> PAT disable         Disabled   BIOS
+ D    D     MTRR -> PAT disable         Disabled    -
+ -    np/E  PAT  -> PAT disable         Disabled   BIOS
+ -    np/D  PAT  -> PAT disable         Disabled    -
+ E    !P/E  MTRR -> PAT init            Disabled   BIOS
+ D    !P/E  MTRR -> PAT disable         Disabled   BIOS
+ !M   !P/E  MTRR stub -> PAT disable    Disabled   BIOS
+
+ Legend
+ ------------------------------------------------
+ E         Feature enabled in CPU
+ D	   Feature disabled/unsupported in CPU
+ np	   "nopat" boot option specified
+ !P	   CONFIG_X86_PAT option unset
+ !M	   CONFIG_MTRR option unset
+ Enabled   PAT state set to enable
+ Disabled  PAT state set to disable
+ OS        PAT initializes PAT MSR with OS setting
+ BIOS      PAT keeps PAT MSR with BIOS setting
+

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Ingo Molnar]

* Toshi Kani <toshi.kani@hpe.com> wrote:

> A Xorg failure on qemu32 was reported as a regression [1] caused by
> 'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")'.
> This patch-set fixes the regression.
> 
> Negative effects of this regression were two failures [2] in Xorg on
> QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were triggered
> by the fact that its virtual CPU does not support MTRR.
>  #1. copy_process() failed in the check in reserve_pfn_range()
>  #2. error path in copy_process() then hit WARN_ON_ONCE in
>      untrack_pfn().
> 
> These negative effects are caused by two separate bugs, but they can be
> addressed in separate patches.  This patch-set addresses the root cause,
> a long-standing PAT initialization issue.
> 
> Please see the changelog in patch 4/7 for the details of the issue.
> 
> - Patch 1-2 make necessary enhancement to PAT for the fix without
>   breaking Xen.
> - Patch 3 is cleanup.
> - Patch 4 fixes the regression.
> - Patch 5 fixes an MTRR issue related with PAT init.
> - Patch 6 removes PAT init code from Xen.
> - Patch 7 adds PAT init to documentation.
> 
> [1]: https://lkml.org/lkml/2016/3/3/828
> [2]: https://lkml.org/lkml/2016/3/4/775

The changelogs are much improved, I've applied these patches to tip:x86/mm,
thanks Toshi!

> I'd appreciate if someone can test this patch-set on Xen to verify that
> there is no change in "x86/PAT: Configuration [0-7] .." message in dmesg.

So I don't have a Xen setup, but hopefully such testing will happen once these 
changes show up in linux-next, tomorrow or so.

Thanks,

	Ingo

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Toshi Kani]

On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
> * Toshi Kani <toshi.kani@hpe.com> wrote:
> 
> > A Xorg failure on qemu32 was reported as a regression [1] caused by
> > 'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")'.
> > This patch-set fixes the regression.
> > 
> > Negative effects of this regression were two failures [2] in Xorg on
> > QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were triggered
> > by the fact that its virtual CPU does not support MTRR.
> >  #1. copy_process() failed in the check in reserve_pfn_range()
> >  #2. error path in copy_process() then hit WARN_ON_ONCE in
> >      untrack_pfn().
> > 
> > These negative effects are caused by two separate bugs, but they can be
> > addressed in separate patches.  This patch-set addresses the root
> > cause, a long-standing PAT initialization issue.
> > 
> > Please see the changelog in patch 4/7 for the details of the issue.
> > 
> > - Patch 1-2 make necessary enhancement to PAT for the fix without
> >   breaking Xen.
> > - Patch 3 is cleanup.
> > - Patch 4 fixes the regression.
> > - Patch 5 fixes an MTRR issue related with PAT init.
> > - Patch 6 removes PAT init code from Xen.
> > - Patch 7 adds PAT init to documentation.
> > 
> > [1]: https://lkml.org/lkml/2016/3/3/828
> > [2]: https://lkml.org/lkml/2016/3/4/775
> 
> The changelogs are much improved, I've applied these patches to
> tip:x86/mm, thanks Toshi!

Great! Thanks for all valuable comments!

> > I'd appreciate if someone can test this patch-set on Xen to verify that
> > there is no change in "x86/PAT: Configuration [0-7] .." message in
> > dmesg.
> 
> So I don't have a Xen setup, but hopefully such testing will happen once
> these changes show up in linux-next, tomorrow or so.

I will address if any issue is found in testing.

-Toshi

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Boris Ostrovsky]

On 03/29/2016 10:19 AM, Toshi Kani wrote:
> On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
>
>>> I'd appreciate if someone can test this patch-set on Xen to verify that
>>> there is no change in "x86/PAT: Configuration [0-7] .." message in
>>> dmesg.
>> So I don't have a Xen setup, but hopefully such testing will happen once
>> these changes show up in linux-next, tomorrow or so.
> I will address if any issue is found in testing.

I ran a subset of out nightly test. Nobody died.

So this all looks good. (It actually may have also fixed another bug 
that was reported recently by Olaf, copied here)

-boris

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Toshi Kani]

On Tue, 2016-03-29 at 10:46 -0400, Boris Ostrovsky wrote:
> On 03/29/2016 10:19 AM, Toshi Kani wrote:
> > On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
> > 
> > > > I'd appreciate if someone can test this patch-set on Xen to verify
> > > > that there is no change in "x86/PAT: Configuration [0-7] .."
> > > > message in dmesg.
> > > So I don't have a Xen setup, but hopefully such testing will happen
> > > once these changes show up in linux-next, tomorrow or so.
> > I will address if any issue is found in testing.
> 
> I ran a subset of out nightly test. Nobody died.
> 
> So this all looks good. (It actually may have also fixed another bug 
> that was reported recently by Olaf, copied here)

Cool! Thanks Boris!
-Toshi

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Luis R. Rodriguez]

On Tue, Mar 29, 2016 at 8:49 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
> On Tue, 2016-03-29 at 10:46 -0400, Boris Ostrovsky wrote:
>> On 03/29/2016 10:19 AM, Toshi Kani wrote:
>> > On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
>> >
>> > > > I'd appreciate if someone can test this patch-set on Xen to verify
>> > > > that there is no change in "x86/PAT: Configuration [0-7] .."
>> > > > message in dmesg.
>> > > So I don't have a Xen setup, but hopefully such testing will happen
>> > > once these changes show up in linux-next, tomorrow or so.
>> > I will address if any issue is found in testing.
>>
>> I ran a subset of out nightly test. Nobody died.
>>
>> So this all looks good. (It actually may have also fixed another bug
>> that was reported recently by Olaf, copied here)
>
> Cool! Thanks Boris!

Hoping Boris or someone on the Xen front would test this prior to
merging helps but it also slows us down, a while ago we discussed the
possibility of getting Linux Xen guests automatically tested as part
of 0-day, this way then when a developer (in this case Toshi) pushes
to his own tree, he'd be able to just sit and wait for the results,
without having to hope Boris or someone goes out and tests.

Its a major undertaking to get Linux Xen guests boot strapped into
0-day, however such prospects were raised a while ago and it seems we
may be able to get there. Just wanted to send a reminder about this
possibility, and highlight this patch set as an ideal candidate where
a proactive test could have helped as well. I proactively caught the
original Xen issue, but git logs shows we are not doing so great in
this area, so any help on the Xen side as well to help with 0-day
integration would be appreciated.

I'll follow up on another thread on that.

 Luis

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Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Konrad Rzeszutek Wilk]

On Wed, Mar 30, 2016 at 11:02:13AM -0700, Luis R. Rodriguez wrote:
> On Tue, Mar 29, 2016 at 8:49 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
> > On Tue, 2016-03-29 at 10:46 -0400, Boris Ostrovsky wrote:
> >> On 03/29/2016 10:19 AM, Toshi Kani wrote:
> >> > On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
> >> >
> >> > > > I'd appreciate if someone can test this patch-set on Xen to verify
> >> > > > that there is no change in "x86/PAT: Configuration [0-7] .."
> >> > > > message in dmesg.
> >> > > So I don't have a Xen setup, but hopefully such testing will happen
> >> > > once these changes show up in linux-next, tomorrow or so.
> >> > I will address if any issue is found in testing.
> >>
> >> I ran a subset of out nightly test. Nobody died.
> >>
> >> So this all looks good. (It actually may have also fixed another bug
> >> that was reported recently by Olaf, copied here)
> >
> > Cool! Thanks Boris!
> 
> Hoping Boris or someone on the Xen front would test this prior to
> merging helps but it also slows us down, a while ago we discussed the

Boris did test it _before_ it was merged.

> possibility of getting Linux Xen guests automatically tested as part
> of 0-day, this way then when a developer (in this case Toshi) pushes
> to his own tree, he'd be able to just sit and wait for the results,
> without having to hope Boris or someone goes out and tests.

In Fedora you just need to do:

#yum install xen
#reboot
And pick the Xen option. 

Probably the same thing with Debian and Ubuntu - just 'apt-get install xen'

> 
> Its a major undertaking to get Linux Xen guests boot strapped into

It is?

> 0-day, however such prospects were raised a while ago and it seems we
> may be able to get there. Just wanted to send a reminder about this
> possibility, and highlight this patch set as an ideal candidate where
> a proactive test could have helped as well. I proactively caught the
> original Xen issue, but git logs shows we are not doing so great in
> this area, so any help on the Xen side as well to help with 0-day
> integration would be appreciated.
> 
> I'll follow up on another thread on that.

Sure. It never hurts to have more coverage.
> 
>  Luis
> 
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> http://lists.xen.org/xen-devel

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Re: [LKP] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Luis R. Rodriguez]

On Wed, Mar 30, 2016 at 11:58 AM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
> On Wed, Mar 30, 2016 at 11:02:13AM -0700, Luis R. Rodriguez wrote:
>> On Tue, Mar 29, 2016 at 8:49 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
>> > On Tue, 2016-03-29 at 10:46 -0400, Boris Ostrovsky wrote:
>> >> On 03/29/2016 10:19 AM, Toshi Kani wrote:
>> >> > On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
>> >> >
>> >> > > > I'd appreciate if someone can test this patch-set on Xen to verify
>> >> > > > that there is no change in "x86/PAT: Configuration [0-7] .."
>> >> > > > message in dmesg.
>> >> > > So I don't have a Xen setup, but hopefully such testing will happen
>> >> > > once these changes show up in linux-next, tomorrow or so.
>> >> > I will address if any issue is found in testing.
>> >>
>> >> I ran a subset of out nightly test. Nobody died.
>> >>
>> >> So this all looks good. (It actually may have also fixed another bug
>> >> that was reported recently by Olaf, copied here)
>> >
>> > Cool! Thanks Boris!
>>
>> Hoping Boris or someone on the Xen front would test this prior to
>> merging helps but it also slows us down, a while ago we discussed the
>
> Boris did test it _before_ it was merged.

Yes, my point being that we should not need Boris to test collateral
Xen patches.

>> possibility of getting Linux Xen guests automatically tested as part
>> of 0-day, this way then when a developer (in this case Toshi) pushes
>> to his own tree, he'd be able to just sit and wait for the results,
>> without having to hope Boris or someone goes out and tests.
>
> In Fedora you just need to do:
>
> #yum install xen
> #reboot
> And pick the Xen option.
>
> Probably the same thing with Debian and Ubuntu - just 'apt-get install xen'

We can't expect everyone to do that.

>> Its a major undertaking to get Linux Xen guests boot strapped into 0-day,
>
> It is?

If its really trivial then you give me the impression you can help
with its integration. 0-day is open after all.

>> however such prospects were raised a while ago and it seems we
>> may be able to get there. Just wanted to send a reminder about this
>> possibility, and highlight this patch set as an ideal candidate where
>> a proactive test could have helped as well. I proactively caught the
>> original Xen issue, but git logs shows we are not doing so great in
>> this area, so any help on the Xen side as well to help with 0-day
>> integration would be appreciated.
>>
>> I'll follow up on another thread on that.
>
> Sure. It never hurts to have more coverage.

Great.

  Luis

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Re: [LKP] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Konrad Rzeszutek Wilk]

On Wed, Mar 30, 2016 at 01:10:29PM -0700, Luis R. Rodriguez wrote:
> On Wed, Mar 30, 2016 at 11:58 AM, Konrad Rzeszutek Wilk
> <konrad.wilk@oracle.com> wrote:
> > On Wed, Mar 30, 2016 at 11:02:13AM -0700, Luis R. Rodriguez wrote:
> >> On Tue, Mar 29, 2016 at 8:49 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
> >> > On Tue, 2016-03-29 at 10:46 -0400, Boris Ostrovsky wrote:
> >> >> On 03/29/2016 10:19 AM, Toshi Kani wrote:
> >> >> > On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
> >> >> >
> >> >> > > > I'd appreciate if someone can test this patch-set on Xen to verify
> >> >> > > > that there is no change in "x86/PAT: Configuration [0-7] .."
> >> >> > > > message in dmesg.
> >> >> > > So I don't have a Xen setup, but hopefully such testing will happen
> >> >> > > once these changes show up in linux-next, tomorrow or so.
> >> >> > I will address if any issue is found in testing.
> >> >>
> >> >> I ran a subset of out nightly test. Nobody died.
> >> >>
> >> >> So this all looks good. (It actually may have also fixed another bug
> >> >> that was reported recently by Olaf, copied here)
> >> >
> >> > Cool! Thanks Boris!
> >>
> >> Hoping Boris or someone on the Xen front would test this prior to
> >> merging helps but it also slows us down, a while ago we discussed the
> >
> > Boris did test it _before_ it was merged.
> 
> Yes, my point being that we should not need Boris to test collateral
> Xen patches.

/me scratches his head.

Are you saying that you expect Xen maintainers to _NOT_ test Xen related
patches? Especially ones they have been involved with?

> 
> >> possibility of getting Linux Xen guests automatically tested as part
> >> of 0-day, this way then when a developer (in this case Toshi) pushes
> >> to his own tree, he'd be able to just sit and wait for the results,
> >> without having to hope Boris or someone goes out and tests.
> >
> > In Fedora you just need to do:
> >
> > #yum install xen
> > #reboot
> > And pick the Xen option.
> >
> > Probably the same thing with Debian and Ubuntu - just 'apt-get install xen'
> 
> We can't expect everyone to do that.
> 
> >> Its a major undertaking to get Linux Xen guests boot strapped into 0-day,
> >
> > It is?
> 
> If its really trivial then you give me the impression you can help
> with its integration. 0-day is open after all.

I have no clue on how the 0-day works - hence my question. I would be more than
happy to help once free time lines up.

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Re: [LKP] [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

[Luis R. Rodriguez]

On Wed, Mar 30, 2016 at 1:29 PM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
> On Wed, Mar 30, 2016 at 01:10:29PM -0700, Luis R. Rodriguez wrote:
>
> Are you saying that you expect Xen maintainers to _NOT_ test Xen related
> patches? Especially ones they have been involved with?

Of course not, I'm saying we have a bottleneck on development if we
need to wait for Xen patches to be tested, and we can do better if we
had 0-day testing this for us. In this case it was *me* who brought up
the issue of a Xen conflict early, and later through other iterations
Toshi addressed this, given we have the technology and bandwidth to do
more testing with 0-day we should not have to count on me or others to
do the proactive review to ensure there is no Xen conflict, or on
Boris for final confirmation. Its a nobrainer the value of integration
of Xen with 0-day.

>> If its really trivial then you give me the impression you can help
>> with its integration. 0-day is open after all.
>
> I have no clue on how the 0-day works - hence my question. I would be more than
> happy to help once free time lines up.

Great.

  Luis

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