[PATCH 0/3] x86: Full support of PAT

[PATCH 0/3] x86: Full support of PAT

[Juergen Gross]

The x86 architecture offers via the PAT (Page Attribute Table) a way to
specify different caching modes in page table entries. The PAT MSR contains
8 entries each specifying one of 6 possible cache modes. A pte references one
of those entries via 3 bits: _PAGE_PAT, _PAGE_PWT and _PAGE_PCD.

The Linux kernel currently supports only 4 different cache modes. The PAT MSR
is set up in a way that the setting of _PAGE_PAT in a pte doesn't matter: the
top 4 entries in the PAT MSR are the same as the 4 lower entries.

This results in the kernel not supporting e.g. write-through mode. Especially
this cache mode would speed up drivers of video cards which now have to use
uncached accesses.

OTOH some old processors (Pentium) don't support PAT correctly and the Xen
hypervisor has been using a different PAT MSR configuration for some time now
and can't change that as this setting is part of the ABI.

This patch set abstracts the cache mode from the pte and introduces tables to
translate between cache mode and pte bits (the default cache mode "write back"
is hard-wired to PAT entry 0). The tables are statically initialized with
values being compatible to old processors and current usage. As soon as the
PAT MSR is changed (or - in case of Xen - is read at boot time) the tables are
changed accordingly. Requests of mappings with special cache modes are always
possible now, in case they are not supported there will be a fallback to a
compatible but slower mode.

Summing it up, this patch set adds the following features:
- capability to support WT and WP cache modes on processors with full PAT
  support
- processors with no or uncorrect PAT support are still working as today, even
  if WT or WP cache mode are selected by drivers for some pages
- reduction of Xen special handling regarding cache mode

Changes since RFC:
- renamed functions and variables as suggested by Toshi Kani
- corrected cache mode bits for WT and WP
- modified handling of PAT MSR write under Xen as suggested by Jan Beulich


Juergen Gross (3):
  x86: Make page cache mode a real type
  x86: Enable PAT to use cache mode translation tables
  Support Xen pv-domains using PAT

 arch/x86/include/asm/cacheflush.h         |  38 ++++---
 arch/x86/include/asm/fb.h                 |   6 +-
 arch/x86/include/asm/io.h                 |   2 +-
 arch/x86/include/asm/pat.h                |   7 +-
 arch/x86/include/asm/pgtable.h            |  19 ++--
 arch/x86/include/asm/pgtable_types.h      |  96 ++++++++++++----
 arch/x86/mm/dump_pagetables.c             |  24 ++--
 arch/x86/mm/init.c                        |  37 ++++++
 arch/x86/mm/init_64.c                     |   9 +-
 arch/x86/mm/iomap_32.c                    |  15 ++-
 arch/x86/mm/ioremap.c                     |  63 ++++++-----
 arch/x86/mm/pageattr.c                    |  84 ++++++++------
 arch/x86/mm/pat.c                         | 180 +++++++++++++++++++-----------
 arch/x86/mm/pat_internal.h                |  22 ++--
 arch/x86/mm/pat_rbtree.c                  |   8 +-
 arch/x86/pci/i386.c                       |   4 +-
 arch/x86/xen/enlighten.c                  |  11 +-
 arch/x86/xen/mmu.c                        |  52 +++------
 arch/x86/xen/xen-ops.h                    |   1 +
 drivers/video/fbdev/gbefb.c               |   3 +-
 drivers/video/fbdev/vermilion/vermilion.c |   6 +-
 include/linux/mm.h                        |   1 +
 22 files changed, 431 insertions(+), 257 deletions(-)

-- 
1.8.4.5

[PATCH 1/3] x86: Make page cache mode a real type

[Juergen Gross]

At the moment there are a lot of places that handle setting or getting
the page cache mode by treating the pgprot bits equal to the cache mode.
This is only true because there are a lot of assumptions about the setup
of the PAT MSR. Otherwise the cache type needs to get translated into
pgprot bits and vice versa.

This patch tries to prepare for that by introducing a seperate type
for the cache mode and adding functions to translate between those and pgprot
values.

To avoid too much performance penalty the translation between cache mode
and pgprot values is done via tables which contain the relevant information.
Write-back cache mode is hard-wired to be 0, all other modes are configurable
via those tables. For large pages there are translation functions as the
PAT bit is located at different positions in the ptes of 4k and large pages.

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/include/asm/cacheflush.h         |  38 +++++----
 arch/x86/include/asm/fb.h                 |   6 +-
 arch/x86/include/asm/io.h                 |   2 +-
 arch/x86/include/asm/pat.h                |   6 +-
 arch/x86/include/asm/pgtable.h            |  19 ++---
 arch/x86/include/asm/pgtable_types.h      |  92 +++++++++++++++++-----
 arch/x86/mm/dump_pagetables.c             |  24 +++---
 arch/x86/mm/init.c                        |  29 +++++++
 arch/x86/mm/init_64.c                     |   9 ++-
 arch/x86/mm/iomap_32.c                    |  15 ++--
 arch/x86/mm/ioremap.c                     |  63 ++++++++-------
 arch/x86/mm/pageattr.c                    |  84 ++++++++++++--------
 arch/x86/mm/pat.c                         | 126 +++++++++++++++---------------
 arch/x86/mm/pat_internal.h                |  22 +++---
 arch/x86/mm/pat_rbtree.c                  |   8 +-
 arch/x86/pci/i386.c                       |   4 +-
 drivers/video/fbdev/gbefb.c               |   3 +-
 drivers/video/fbdev/vermilion/vermilion.c |   6 +-
 18 files changed, 344 insertions(+), 212 deletions(-)

diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
index 9863ee3..157644b 100644
--- a/arch/x86/include/asm/cacheflush.h
+++ b/arch/x86/include/asm/cacheflush.h
@@ -9,10 +9,10 @@
 /*
  * X86 PAT uses page flags WC and Uncached together to keep track of
  * memory type of pages that have backing page struct. X86 PAT supports 3
- * different memory types, _PAGE_CACHE_WB, _PAGE_CACHE_WC and
- * _PAGE_CACHE_UC_MINUS and fourth state where page's memory type has not
+ * different memory types, _PAGE_CACHE_MODE_WB, _PAGE_CACHE_MODE_WC and
+ * _PAGE_CACHE_MODE_UC_MINUS and fourth state where page's memory type has not
  * been changed from its default (value of -1 used to denote this).
- * Note we do not support _PAGE_CACHE_UC here.
+ * Note we do not support _PAGE_CACHE_MODE_UC here.
  */
 
 #define _PGMT_DEFAULT		0
@@ -22,36 +22,40 @@
 #define _PGMT_MASK		(1UL << PG_uncached | 1UL << PG_arch_1)
 #define _PGMT_CLEAR_MASK	(~_PGMT_MASK)
 
-static inline unsigned long get_page_memtype(struct page *pg)
+static inline enum page_cache_mode get_page_memtype(struct page *pg)
 {
 	unsigned long pg_flags = pg->flags & _PGMT_MASK;
 
 	if (pg_flags == _PGMT_DEFAULT)
 		return -1;
 	else if (pg_flags == _PGMT_WC)
-		return _PAGE_CACHE_WC;
+		return _PAGE_CACHE_MODE_WC;
 	else if (pg_flags == _PGMT_UC_MINUS)
-		return _PAGE_CACHE_UC_MINUS;
+		return _PAGE_CACHE_MODE_UC_MINUS;
 	else
-		return _PAGE_CACHE_WB;
+		return _PAGE_CACHE_MODE_WB;
 }
 
-static inline void set_page_memtype(struct page *pg, unsigned long memtype)
+static inline void set_page_memtype(struct page *pg,
+				    enum page_cache_mode memtype)
 {
-	unsigned long memtype_flags = _PGMT_DEFAULT;
+	unsigned long memtype_flags;
 	unsigned long old_flags;
 	unsigned long new_flags;
 
 	switch (memtype) {
-	case _PAGE_CACHE_WC:
+	case _PAGE_CACHE_MODE_WC:
 		memtype_flags = _PGMT_WC;
 		break;
-	case _PAGE_CACHE_UC_MINUS:
+	case _PAGE_CACHE_MODE_UC_MINUS:
 		memtype_flags = _PGMT_UC_MINUS;
 		break;
-	case _PAGE_CACHE_WB:
+	case _PAGE_CACHE_MODE_WB:
 		memtype_flags = _PGMT_WB;
 		break;
+	default:
+		memtype_flags = _PGMT_DEFAULT;
+		break;
 	}
 
 	do {
@@ -60,8 +64,14 @@ static inline void set_page_memtype(struct page *pg, unsigned long memtype)
 	} while (cmpxchg(&pg->flags, old_flags, new_flags) != old_flags);
 }
 #else
-static inline unsigned long get_page_memtype(struct page *pg) { return -1; }
-static inline void set_page_memtype(struct page *pg, unsigned long memtype) { }
+static inline enum page_cache_mode get_page_memtype(struct page *pg)
+{
+	return -1;
+}
+static inline void set_page_memtype(struct page *pg,
+				    enum page_cache_mode memtype)
+{
+}
 #endif
 
 /*
diff --git a/arch/x86/include/asm/fb.h b/arch/x86/include/asm/fb.h
index 2519d06..0902a50 100644
--- a/arch/x86/include/asm/fb.h
+++ b/arch/x86/include/asm/fb.h
@@ -8,8 +8,12 @@
 static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
 				unsigned long off)
 {
+	unsigned long prot;
+
+	prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
 	if (boot_cpu_data.x86 > 3)
-		pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
+		pgprot_val(vma->vm_page_prot) =
+			prot | cachemode2protval(_PAGE_CACHE_MODE_UC);
 }
 
 extern int fb_is_primary_device(struct fb_info *info);
diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index b8237d8..71b9e65 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -314,7 +314,7 @@ extern void *xlate_dev_mem_ptr(unsigned long phys);
 extern void unxlate_dev_mem_ptr(unsigned long phys, void *addr);
 
 extern int ioremap_change_attr(unsigned long vaddr, unsigned long size,
-				unsigned long prot_val);
+				enum page_cache_mode pcm);
 extern void __iomem *ioremap_wc(resource_size_t offset, unsigned long size);
 
 extern bool is_early_ioremap_ptep(pte_t *ptep);
diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index e2c1668..150407a 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -13,14 +13,14 @@ static const int pat_enabled;
 extern void pat_init(void);
 
 extern int reserve_memtype(u64 start, u64 end,
-		unsigned long req_type, unsigned long *ret_type);
+		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
 extern int free_memtype(u64 start, u64 end);
 
 extern int kernel_map_sync_memtype(u64 base, unsigned long size,
-		unsigned long flag);
+		enum page_cache_mode pcm);
 
 int io_reserve_memtype(resource_size_t start, resource_size_t end,
-			unsigned long *type);
+			enum page_cache_mode *pcm);
 
 void io_free_memtype(resource_size_t start, resource_size_t end);
 
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 0ec0560..055047f 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -9,9 +9,10 @@
 /*
  * Macro to mark a page protection value as UC-
  */
-#define pgprot_noncached(prot)					\
-	((boot_cpu_data.x86 > 3)				\
-	 ? (__pgprot(pgprot_val(prot) | _PAGE_CACHE_UC_MINUS))	\
+#define pgprot_noncached(prot)						\
+	((boot_cpu_data.x86 > 3)					\
+	 ? (__pgprot(pgprot_val(prot) |					\
+		     cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS)))	\
 	 : (prot))
 
 #ifndef __ASSEMBLY__
@@ -399,8 +400,8 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 #define canon_pgprot(p) __pgprot(massage_pgprot(p))
 
 static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
-					 unsigned long flags,
-					 unsigned long new_flags)
+					 enum page_cache_mode pcm,
+					 enum page_cache_mode new_pcm)
 {
 	/*
 	 * PAT type is always WB for untracked ranges, so no need to check.
@@ -414,10 +415,10 @@ static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
 	 * - request is uncached, return cannot be write-back
 	 * - request is write-combine, return cannot be write-back
 	 */
-	if ((flags == _PAGE_CACHE_UC_MINUS &&
-	     new_flags == _PAGE_CACHE_WB) ||
-	    (flags == _PAGE_CACHE_WC &&
-	     new_flags == _PAGE_CACHE_WB)) {
+	if ((pcm == _PAGE_CACHE_MODE_UC_MINUS &&
+	     new_pcm == _PAGE_CACHE_MODE_WB) ||
+	    (pcm == _PAGE_CACHE_MODE_WC &&
+	     new_pcm == _PAGE_CACHE_MODE_WB)) {
 		return 0;
 	}
 
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index f216963..0d38511 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -129,11 +129,28 @@
 			 _PAGE_SOFT_DIRTY | _PAGE_NUMA)
 #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_NUMA)
 
-#define _PAGE_CACHE_MASK	(_PAGE_PCD | _PAGE_PWT)
-#define _PAGE_CACHE_WB		(0)
-#define _PAGE_CACHE_WC		(_PAGE_PWT)
-#define _PAGE_CACHE_UC_MINUS	(_PAGE_PCD)
-#define _PAGE_CACHE_UC		(_PAGE_PCD | _PAGE_PWT)
+/*
+ * The cache modes defined here are used to translate between pure SW usage
+ * and the HW defined cache mode bits and/or PAT entries.
+ *
+ * The resulting bits for PWT, PCD and PAT should be chosen in a way
+ * to have the WB mode at index 0 (all bits clear). This is the default
+ * right now and likely would break too much if changed.
+ */
+#ifndef __ASSEMBLY__
+enum page_cache_mode {
+	_PAGE_CACHE_MODE_WB = 0,
+	_PAGE_CACHE_MODE_WC = 1,
+	_PAGE_CACHE_MODE_UC_MINUS = 2,
+	_PAGE_CACHE_MODE_UC = 3,
+	_PAGE_CACHE_MODE_WT = 4,
+	_PAGE_CACHE_MODE_WP = 5,
+	_PAGE_CACHE_MODE_NUM = 8
+};
+#endif
+
+#define _PAGE_CACHE_MASK	(_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)
+#define _PAGE_NOCACHE		(cachemode2protval(_PAGE_CACHE_MODE_UC))
 
 #define PAGE_NONE	__pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
 #define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
@@ -157,41 +174,27 @@
 
 #define __PAGE_KERNEL_RO		(__PAGE_KERNEL & ~_PAGE_RW)
 #define __PAGE_KERNEL_RX		(__PAGE_KERNEL_EXEC & ~_PAGE_RW)
-#define __PAGE_KERNEL_EXEC_NOCACHE	(__PAGE_KERNEL_EXEC | _PAGE_PCD | _PAGE_PWT)
-#define __PAGE_KERNEL_WC		(__PAGE_KERNEL | _PAGE_CACHE_WC)
-#define __PAGE_KERNEL_NOCACHE		(__PAGE_KERNEL | _PAGE_PCD | _PAGE_PWT)
-#define __PAGE_KERNEL_UC_MINUS		(__PAGE_KERNEL | _PAGE_PCD)
+#define __PAGE_KERNEL_NOCACHE		(__PAGE_KERNEL | _PAGE_NOCACHE)
 #define __PAGE_KERNEL_VSYSCALL		(__PAGE_KERNEL_RX | _PAGE_USER)
 #define __PAGE_KERNEL_VVAR		(__PAGE_KERNEL_RO | _PAGE_USER)
-#define __PAGE_KERNEL_VVAR_NOCACHE	(__PAGE_KERNEL_VVAR | _PAGE_PCD | _PAGE_PWT)
 #define __PAGE_KERNEL_LARGE		(__PAGE_KERNEL | _PAGE_PSE)
-#define __PAGE_KERNEL_LARGE_NOCACHE	(__PAGE_KERNEL | _PAGE_CACHE_UC | _PAGE_PSE)
 #define __PAGE_KERNEL_LARGE_EXEC	(__PAGE_KERNEL_EXEC | _PAGE_PSE)
 
 #define __PAGE_KERNEL_IO		(__PAGE_KERNEL | _PAGE_IOMAP)
 #define __PAGE_KERNEL_IO_NOCACHE	(__PAGE_KERNEL_NOCACHE | _PAGE_IOMAP)
-#define __PAGE_KERNEL_IO_UC_MINUS	(__PAGE_KERNEL_UC_MINUS | _PAGE_IOMAP)
-#define __PAGE_KERNEL_IO_WC		(__PAGE_KERNEL_WC | _PAGE_IOMAP)
 
 #define PAGE_KERNEL			__pgprot(__PAGE_KERNEL)
 #define PAGE_KERNEL_RO			__pgprot(__PAGE_KERNEL_RO)
 #define PAGE_KERNEL_EXEC		__pgprot(__PAGE_KERNEL_EXEC)
 #define PAGE_KERNEL_RX			__pgprot(__PAGE_KERNEL_RX)
-#define PAGE_KERNEL_WC			__pgprot(__PAGE_KERNEL_WC)
 #define PAGE_KERNEL_NOCACHE		__pgprot(__PAGE_KERNEL_NOCACHE)
-#define PAGE_KERNEL_UC_MINUS		__pgprot(__PAGE_KERNEL_UC_MINUS)
-#define PAGE_KERNEL_EXEC_NOCACHE	__pgprot(__PAGE_KERNEL_EXEC_NOCACHE)
 #define PAGE_KERNEL_LARGE		__pgprot(__PAGE_KERNEL_LARGE)
-#define PAGE_KERNEL_LARGE_NOCACHE	__pgprot(__PAGE_KERNEL_LARGE_NOCACHE)
 #define PAGE_KERNEL_LARGE_EXEC		__pgprot(__PAGE_KERNEL_LARGE_EXEC)
 #define PAGE_KERNEL_VSYSCALL		__pgprot(__PAGE_KERNEL_VSYSCALL)
 #define PAGE_KERNEL_VVAR		__pgprot(__PAGE_KERNEL_VVAR)
-#define PAGE_KERNEL_VVAR_NOCACHE	__pgprot(__PAGE_KERNEL_VVAR_NOCACHE)
 
 #define PAGE_KERNEL_IO			__pgprot(__PAGE_KERNEL_IO)
 #define PAGE_KERNEL_IO_NOCACHE		__pgprot(__PAGE_KERNEL_IO_NOCACHE)
-#define PAGE_KERNEL_IO_UC_MINUS		__pgprot(__PAGE_KERNEL_IO_UC_MINUS)
-#define PAGE_KERNEL_IO_WC		__pgprot(__PAGE_KERNEL_IO_WC)
 
 /*         xwr */
 #define __P000	PAGE_NONE
@@ -328,6 +331,55 @@ static inline pteval_t pte_flags(pte_t pte)
 #define pgprot_val(x)	((x).pgprot)
 #define __pgprot(x)	((pgprot_t) { (x) } )
 
+extern uint16_t __cachemode2pte_tbl[_PAGE_CACHE_MODE_NUM];
+extern uint8_t __pte2cachemode_tbl[8];
+
+#define __pte2cm_idx(cb)				\
+	((((cb) >> (_PAGE_BIT_PAT - 2)) & 4) |		\
+	 (((cb) >> (_PAGE_BIT_PCD - 1)) & 2) |		\
+	 (((cb) >> _PAGE_BIT_PWT) & 1))
+
+static inline unsigned long cachemode2protval(enum page_cache_mode pcm)
+{
+	if (likely(pcm == 0))
+		return 0;
+	return __cachemode2pte_tbl[pcm];
+}
+static inline pgprot_t cachemode2pgprot(enum page_cache_mode pcm)
+{
+	return __pgprot(cachemode2protval(pcm));
+}
+static inline enum page_cache_mode pgprot2cachemode(pgprot_t pgprot)
+{
+	unsigned long masked;
+
+	masked = pgprot_val(pgprot) & _PAGE_CACHE_MASK;
+	if (likely(masked == 0))
+		return 0;
+	return __pte2cachemode_tbl[__pte2cm_idx(masked)];
+}
+static inline pgprot_t pgprot_4k_2_large(pgprot_t pgprot)
+{
+	pgprot_t new;
+	unsigned long val;
+
+	val = pgprot_val(pgprot);
+	pgprot_val(new) = (val & ~(_PAGE_PAT | _PAGE_PAT_LARGE)) |
+		((val & _PAGE_PAT) << (_PAGE_BIT_PAT_LARGE - _PAGE_BIT_PAT));
+	return new;
+}
+static inline pgprot_t pgprot_large_2_4k(pgprot_t pgprot)
+{
+	pgprot_t new;
+	unsigned long val;
+
+	val = pgprot_val(pgprot);
+	pgprot_val(new) = (val & ~(_PAGE_PAT | _PAGE_PAT_LARGE)) |
+		((val & _PAGE_PAT_LARGE) >>
+		 (_PAGE_BIT_PAT_LARGE - _PAGE_BIT_PAT));
+	return new;
+}
+
 
 typedef struct page *pgtable_t;
 
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 167ffca..52a336a 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -122,7 +122,7 @@ static void printk_prot(struct seq_file *m, pgprot_t prot, int level, bool dmsg)
 
 	if (!pgprot_val(prot)) {
 		/* Not present */
-		pt_dump_cont_printf(m, dmsg, "                          ");
+		pt_dump_cont_printf(m, dmsg, "                              ");
 	} else {
 		if (pr & _PAGE_USER)
 			pt_dump_cont_printf(m, dmsg, "USR ");
@@ -141,18 +141,16 @@ static void printk_prot(struct seq_file *m, pgprot_t prot, int level, bool dmsg)
 		else
 			pt_dump_cont_printf(m, dmsg, "    ");
 
-		/* Bit 9 has a different meaning on level 3 vs 4 */
-		if (level <= 3) {
-			if (pr & _PAGE_PSE)
-				pt_dump_cont_printf(m, dmsg, "PSE ");
-			else
-				pt_dump_cont_printf(m, dmsg, "    ");
-		} else {
-			if (pr & _PAGE_PAT)
-				pt_dump_cont_printf(m, dmsg, "pat ");
-			else
-				pt_dump_cont_printf(m, dmsg, "    ");
-		}
+		/* Bit 7 has a different meaning on level 3 vs 4 */
+		if (level <= 3 && pr & _PAGE_PSE)
+			pt_dump_cont_printf(m, dmsg, "PSE ");
+		else
+			pt_dump_cont_printf(m, dmsg, "    ");
+		if ((level == 4 && pr & _PAGE_PAT) ||
+		    ((level == 3 || level == 2) && pr & _PAGE_PAT_LARGE))
+			pt_dump_cont_printf(m, dmsg, "pat ");
+		else
+			pt_dump_cont_printf(m, dmsg, "    ");
 		if (pr & _PAGE_GLOBAL)
 			pt_dump_cont_printf(m, dmsg, "GLB ");
 		else
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 66dba36..a9776ba 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -27,6 +27,35 @@
 
 #include "mm_internal.h"
 
+/*
+ * Tables translating between page_cache_type_t and pte encoding.
+ * Minimal supported modes are defined statically, modified if more supported
+ * cache modes are available.
+ * Index into __cachemode2pte_tbl is the cachemode.
+ * Index into __pte2cachemode_tbl are the caching attribute bits of the pte
+ * (_PAGE_PWT, _PAGE_PCD, _PAGE_PAT) at index bit positions 0, 1, 2.
+ */
+uint16_t __cachemode2pte_tbl[_PAGE_CACHE_MODE_NUM] = {
+	[_PAGE_CACHE_MODE_WB]		= 0,
+	[_PAGE_CACHE_MODE_WC]		= _PAGE_PWT,
+	[_PAGE_CACHE_MODE_UC_MINUS]	= _PAGE_PCD,
+	[_PAGE_CACHE_MODE_UC]		= _PAGE_PCD | _PAGE_PWT,
+	[_PAGE_CACHE_MODE_WT]		= _PAGE_PCD,
+	[_PAGE_CACHE_MODE_WP]		= _PAGE_PCD,
+};
+EXPORT_SYMBOL_GPL(__cachemode2pte_tbl);
+uint8_t __pte2cachemode_tbl[8] = {
+	[__pte2cm_idx(0)] = _PAGE_CACHE_MODE_WB,
+	[__pte2cm_idx(_PAGE_PWT)] = _PAGE_CACHE_MODE_WC,
+	[__pte2cm_idx(_PAGE_PCD)] = _PAGE_CACHE_MODE_UC_MINUS,
+	[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD)] = _PAGE_CACHE_MODE_UC,
+	[__pte2cm_idx(_PAGE_PAT)] = _PAGE_CACHE_MODE_WB,
+	[__pte2cm_idx(_PAGE_PWT | _PAGE_PAT)] = _PAGE_CACHE_MODE_WC,
+	[__pte2cm_idx(_PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
+	[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC,
+};
+EXPORT_SYMBOL_GPL(__pte2cachemode_tbl);
+
 static unsigned long __initdata pgt_buf_start;
 static unsigned long __initdata pgt_buf_end;
 static unsigned long __initdata pgt_buf_top;
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 5621c47..201f3d0 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -327,12 +327,15 @@ pte_t * __init populate_extra_pte(unsigned long vaddr)
  * Create large page table mappings for a range of physical addresses.
  */
 static void __init __init_extra_mapping(unsigned long phys, unsigned long size,
-						pgprot_t prot)
+					enum page_cache_mode cache)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
+	pgprot_t prot;
 
+	pgprot_val(prot) = pgprot_val(PAGE_KERNEL_LARGE) |
+		pgprot_val(pgprot_4k_2_large(cachemode2pgprot(cache)));
 	BUG_ON((phys & ~PMD_MASK) || (size & ~PMD_MASK));
 	for (; size; phys += PMD_SIZE, size -= PMD_SIZE) {
 		pgd = pgd_offset_k((unsigned long)__va(phys));
@@ -355,12 +358,12 @@ static void __init __init_extra_mapping(unsigned long phys, unsigned long size,
 
 void __init init_extra_mapping_wb(unsigned long phys, unsigned long size)
 {
-	__init_extra_mapping(phys, size, PAGE_KERNEL_LARGE);
+	__init_extra_mapping(phys, size, _PAGE_CACHE_MODE_WB);
 }
 
 void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
 {
-	__init_extra_mapping(phys, size, PAGE_KERNEL_LARGE_NOCACHE);
+	__init_extra_mapping(phys, size, _PAGE_CACHE_MODE_UC);
 }
 
 /*
diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
index 7b179b4..eb879cf 100644
--- a/arch/x86/mm/iomap_32.c
+++ b/arch/x86/mm/iomap_32.c
@@ -33,17 +33,17 @@ static int is_io_mapping_possible(resource_size_t base, unsigned long size)
 
 int iomap_create_wc(resource_size_t base, unsigned long size, pgprot_t *prot)
 {
-	unsigned long flag = _PAGE_CACHE_WC;
+	enum page_cache_mode pcm = _PAGE_CACHE_MODE_WC;
 	int ret;
 
 	if (!is_io_mapping_possible(base, size))
 		return -EINVAL;
 
-	ret = io_reserve_memtype(base, base + size, &flag);
+	ret = io_reserve_memtype(base, base + size, &pcm);
 	if (ret)
 		return ret;
 
-	*prot = __pgprot(__PAGE_KERNEL | flag);
+	*prot = __pgprot(__PAGE_KERNEL | cachemode2protval(pcm));
 	return 0;
 }
 EXPORT_SYMBOL_GPL(iomap_create_wc);
@@ -73,6 +73,9 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
 /*
  * Map 'pfn' using protections 'prot'
  */
+#define __PAGE_KERNEL_WC	(__PAGE_KERNEL | \
+				 cachemode2protval(_PAGE_CACHE_MODE_WC))
+
 void __iomem *
 iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
 {
@@ -82,12 +85,14 @@ iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
 	 * MTRR is UC or WC.  UC_MINUS gets the real intention, of the
 	 * user, which is "WC if the MTRR is WC, UC if you can't do that."
 	 */
-	if (!pat_enabled && pgprot_val(prot) == pgprot_val(PAGE_KERNEL_WC))
-		prot = PAGE_KERNEL_UC_MINUS;
+	if (!pat_enabled && pgprot_val(prot) == __PAGE_KERNEL_WC)
+		prot = __pgprot(__PAGE_KERNEL |
+				protval_pagemode(_PAGE_CACHE_MODE_UC_MINUS));
 
 	return (void __force __iomem *) kmap_atomic_prot_pfn(pfn, prot);
 }
 EXPORT_SYMBOL_GPL(iomap_atomic_prot_pfn);
+#undef __PAGE_KERNEL_WC
 
 void
 iounmap_atomic(void __iomem *kvaddr)
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index baff1da..885fe44 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -29,20 +29,20 @@
  * conflicts.
  */
 int ioremap_change_attr(unsigned long vaddr, unsigned long size,
-			       unsigned long prot_val)
+			enum page_cache_mode pcm)
 {
 	unsigned long nrpages = size >> PAGE_SHIFT;
 	int err;
 
-	switch (prot_val) {
-	case _PAGE_CACHE_UC:
+	switch (pcm) {
+	case _PAGE_CACHE_MODE_UC:
 	default:
 		err = _set_memory_uc(vaddr, nrpages);
 		break;
-	case _PAGE_CACHE_WC:
+	case _PAGE_CACHE_MODE_WC:
 		err = _set_memory_wc(vaddr, nrpages);
 		break;
-	case _PAGE_CACHE_WB:
+	case _PAGE_CACHE_MODE_WB:
 		err = _set_memory_wb(vaddr, nrpages);
 		break;
 	}
@@ -75,14 +75,14 @@ static int __ioremap_check_ram(unsigned long start_pfn, unsigned long nr_pages,
  * caller shouldn't need to know that small detail.
  */
 static void __iomem *__ioremap_caller(resource_size_t phys_addr,
-		unsigned long size, unsigned long prot_val, void *caller)
+		unsigned long size, enum page_cache_mode pcm, void *caller)
 {
 	unsigned long offset, vaddr;
 	resource_size_t pfn, last_pfn, last_addr;
 	const resource_size_t unaligned_phys_addr = phys_addr;
 	const unsigned long unaligned_size = size;
 	struct vm_struct *area;
-	unsigned long new_prot_val;
+	enum page_cache_mode new_pcm;
 	pgprot_t prot;
 	int retval;
 	void __iomem *ret_addr;
@@ -122,38 +122,40 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 	size = PAGE_ALIGN(last_addr+1) - phys_addr;
 
 	retval = reserve_memtype(phys_addr, (u64)phys_addr + size,
-						prot_val, &new_prot_val);
+						pcm, &new_pcm);
 	if (retval) {
 		printk(KERN_ERR "ioremap reserve_memtype failed %d\n", retval);
 		return NULL;
 	}
 
-	if (prot_val != new_prot_val) {
-		if (!is_new_memtype_allowed(phys_addr, size,
-					    prot_val, new_prot_val)) {
+	if (pcm != new_pcm) {
+		if (!is_new_memtype_allowed(phys_addr, size, pcm, new_pcm)) {
 			printk(KERN_ERR
-		"ioremap error for 0x%llx-0x%llx, requested 0x%lx, got 0x%lx\n",
+		"ioremap error for 0x%llx-0x%llx, requested 0x%x, got 0x%x\n",
 				(unsigned long long)phys_addr,
 				(unsigned long long)(phys_addr + size),
-				prot_val, new_prot_val);
+				pcm, new_pcm);
 			goto err_free_memtype;
 		}
-		prot_val = new_prot_val;
+		pcm = new_pcm;
 	}
 
-	switch (prot_val) {
-	case _PAGE_CACHE_UC:
+	prot = PAGE_KERNEL_IO;
+	switch (pcm) {
+	case _PAGE_CACHE_MODE_UC:
 	default:
-		prot = PAGE_KERNEL_IO_NOCACHE;
+		prot = __pgprot(pgprot_val(prot) |
+				cachemode2protval(_PAGE_CACHE_MODE_UC));
 		break;
-	case _PAGE_CACHE_UC_MINUS:
-		prot = PAGE_KERNEL_IO_UC_MINUS;
+	case _PAGE_CACHE_MODE_UC_MINUS:
+		prot = __pgprot(pgprot_val(prot) |
+				cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS));
 		break;
-	case _PAGE_CACHE_WC:
-		prot = PAGE_KERNEL_IO_WC;
+	case _PAGE_CACHE_MODE_WC:
+		prot = __pgprot(pgprot_val(prot) |
+				cachemode2protval(_PAGE_CACHE_MODE_WC));
 		break;
-	case _PAGE_CACHE_WB:
-		prot = PAGE_KERNEL_IO;
+	case _PAGE_CACHE_MODE_WB:
 		break;
 	}
 
@@ -166,7 +168,7 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 	area->phys_addr = phys_addr;
 	vaddr = (unsigned long) area->addr;
 
-	if (kernel_map_sync_memtype(phys_addr, size, prot_val))
+	if (kernel_map_sync_memtype(phys_addr, size, pcm))
 		goto err_free_area;
 
 	if (ioremap_page_range(vaddr, vaddr + size, phys_addr, prot))
@@ -215,14 +217,14 @@ void __iomem *ioremap_nocache(resource_size_t phys_addr, unsigned long size)
 {
 	/*
 	 * Ideally, this should be:
-	 *	pat_enabled ? _PAGE_CACHE_UC : _PAGE_CACHE_UC_MINUS;
+	 *	pat_enabled ? _PAGE_CACHE_MODE_UC : _PAGE_CACHE_MODE_UC_MINUS;
 	 *
 	 * Till we fix all X drivers to use ioremap_wc(), we will use
 	 * UC MINUS.
 	 */
-	unsigned long val = _PAGE_CACHE_UC_MINUS;
+	enum page_cache_mode pcm = _PAGE_CACHE_MODE_UC_MINUS;
 
-	return __ioremap_caller(phys_addr, size, val,
+	return __ioremap_caller(phys_addr, size, pcm,
 				__builtin_return_address(0));
 }
 EXPORT_SYMBOL(ioremap_nocache);
@@ -240,7 +242,7 @@ EXPORT_SYMBOL(ioremap_nocache);
 void __iomem *ioremap_wc(resource_size_t phys_addr, unsigned long size)
 {
 	if (pat_enabled)
-		return __ioremap_caller(phys_addr, size, _PAGE_CACHE_WC,
+		return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WC,
 					__builtin_return_address(0));
 	else
 		return ioremap_nocache(phys_addr, size);
@@ -249,7 +251,7 @@ EXPORT_SYMBOL(ioremap_wc);
 
 void __iomem *ioremap_cache(resource_size_t phys_addr, unsigned long size)
 {
-	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_WB,
+	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WB,
 				__builtin_return_address(0));
 }
 EXPORT_SYMBOL(ioremap_cache);
@@ -257,7 +259,8 @@ EXPORT_SYMBOL(ioremap_cache);
 void __iomem *ioremap_prot(resource_size_t phys_addr, unsigned long size,
 				unsigned long prot_val)
 {
-	return __ioremap_caller(phys_addr, size, (prot_val & _PAGE_CACHE_MASK),
+	return __ioremap_caller(phys_addr, size,
+				pgprot2cachemode(__pgprot(prot_val)),
 				__builtin_return_address(0));
 }
 EXPORT_SYMBOL(ioremap_prot);
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index ae242a7..6917b39 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -485,14 +485,23 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
 
 	/*
 	 * We are safe now. Check whether the new pgprot is the same:
+	 * Convert protection attributes to 4k-format, as cpa->mask* are set
+	 * up accordingly.
 	 */
 	old_pte = *kpte;
-	old_prot = req_prot = pte_pgprot(old_pte);
+	old_prot = req_prot = pgprot_large_2_4k(pte_pgprot(old_pte));
 
 	pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr);
 	pgprot_val(req_prot) |= pgprot_val(cpa->mask_set);
 
 	/*
+	 * req_prot is in format of 4k pages. It must be converted to large
+	 * page format: the caching mode includes the PAT bit located at
+	 * different bit positions in the two formats.
+	 */
+	req_prot = pgprot_4k_2_large(req_prot);
+
+	/*
 	 * Set the PSE and GLOBAL flags only if the PRESENT flag is
 	 * set otherwise pmd_present/pmd_huge will return true even on
 	 * a non present pmd. The canon_pgprot will clear _PAGE_GLOBAL
@@ -585,13 +594,10 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 
 	paravirt_alloc_pte(&init_mm, page_to_pfn(base));
 	ref_prot = pte_pgprot(pte_clrhuge(*kpte));
-	/*
-	 * If we ever want to utilize the PAT bit, we need to
-	 * update this function to make sure it's converted from
-	 * bit 12 to bit 7 when we cross from the 2MB level to
-	 * the 4K level:
-	 */
-	WARN_ON_ONCE(pgprot_val(ref_prot) & _PAGE_PAT_LARGE);
+
+	/* promote PAT bit to correct position */
+	if (level == PG_LEVEL_2M)
+		ref_prot = pgprot_large_2_4k(ref_prot);
 
 #ifdef CONFIG_X86_64
 	if (level == PG_LEVEL_1G) {
@@ -879,6 +885,7 @@ static int populate_pmd(struct cpa_data *cpa,
 {
 	unsigned int cur_pages = 0;
 	pmd_t *pmd;
+	pgprot_t pmd_pgprot;
 
 	/*
 	 * Not on a 2M boundary?
@@ -910,6 +917,8 @@ static int populate_pmd(struct cpa_data *cpa,
 	if (num_pages == cur_pages)
 		return cur_pages;
 
+	pmd_pgprot = pgprot_4k_2_large(pgprot);
+
 	while (end - start >= PMD_SIZE) {
 
 		/*
@@ -921,7 +930,8 @@ static int populate_pmd(struct cpa_data *cpa,
 
 		pmd = pmd_offset(pud, start);
 
-		set_pmd(pmd, __pmd(cpa->pfn | _PAGE_PSE | massage_pgprot(pgprot)));
+		set_pmd(pmd, __pmd(cpa->pfn | _PAGE_PSE |
+				   massage_pgprot(pmd_pgprot)));
 
 		start	  += PMD_SIZE;
 		cpa->pfn  += PMD_SIZE;
@@ -949,6 +959,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 	pud_t *pud;
 	unsigned long end;
 	int cur_pages = 0;
+	pgprot_t pud_pgprot;
 
 	end = start + (cpa->numpages << PAGE_SHIFT);
 
@@ -986,12 +997,14 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 		return cur_pages;
 
 	pud = pud_offset(pgd, start);
+	pud_pgprot = pgprot_4k_2_large(pgprot);
 
 	/*
 	 * Map everything starting from the Gb boundary, possibly with 1G pages
 	 */
 	while (end - start >= PUD_SIZE) {
-		set_pud(pud, __pud(cpa->pfn | _PAGE_PSE | massage_pgprot(pgprot)));
+		set_pud(pud, __pud(cpa->pfn | _PAGE_PSE |
+				   massage_pgprot(pud_pgprot)));
 
 		start	  += PUD_SIZE;
 		cpa->pfn  += PUD_SIZE;
@@ -1304,12 +1317,6 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 	return 0;
 }
 
-static inline int cache_attr(pgprot_t attr)
-{
-	return pgprot_val(attr) &
-		(_PAGE_PAT | _PAGE_PAT_LARGE | _PAGE_PWT | _PAGE_PCD);
-}
-
 static int change_page_attr_set_clr(unsigned long *addr, int numpages,
 				    pgprot_t mask_set, pgprot_t mask_clr,
 				    int force_split, int in_flag,
@@ -1390,7 +1397,7 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,
 	 * No need to flush, when we did not set any of the caching
 	 * attributes:
 	 */
-	cache = cache_attr(mask_set);
+	cache = !!pgprot2cachemode(mask_set);
 
 	/*
 	 * On success we use CLFLUSH, when the CPU supports it to
@@ -1445,7 +1452,8 @@ int _set_memory_uc(unsigned long addr, int numpages)
 	 * for now UC MINUS. see comments in ioremap_nocache()
 	 */
 	return change_page_attr_set(&addr, numpages,
-				    __pgprot(_PAGE_CACHE_UC_MINUS), 0);
+				    cachemode2pgprot(_PAGE_CACHE_MODE_UC_MINUS),
+				    0);
 }
 
 int set_memory_uc(unsigned long addr, int numpages)
@@ -1456,7 +1464,7 @@ int set_memory_uc(unsigned long addr, int numpages)
 	 * for now UC MINUS. see comments in ioremap_nocache()
 	 */
 	ret = reserve_memtype(__pa(addr), __pa(addr) + numpages * PAGE_SIZE,
-			    _PAGE_CACHE_UC_MINUS, NULL);
+			      _PAGE_CACHE_MODE_UC_MINUS, NULL);
 	if (ret)
 		goto out_err;
 
@@ -1474,7 +1482,7 @@ out_err:
 EXPORT_SYMBOL(set_memory_uc);
 
 static int _set_memory_array(unsigned long *addr, int addrinarray,
-		unsigned long new_type)
+		enum page_cache_mode new_type)
 {
 	int i, j;
 	int ret;
@@ -1490,11 +1498,13 @@ static int _set_memory_array(unsigned long *addr, int addrinarray,
 	}
 
 	ret = change_page_attr_set(addr, addrinarray,
-				    __pgprot(_PAGE_CACHE_UC_MINUS), 1);
+				   cachemode2pgprot(_PAGE_CACHE_MODE_UC_MINUS),
+				   1);
 
-	if (!ret && new_type == _PAGE_CACHE_WC)
+	if (!ret && new_type == _PAGE_CACHE_MODE_WC)
 		ret = change_page_attr_set_clr(addr, addrinarray,
-					       __pgprot(_PAGE_CACHE_WC),
+					       cachemode2pgprot(
+						   _PAGE_CACHE_MODE_WC),
 					       __pgprot(_PAGE_CACHE_MASK),
 					       0, CPA_ARRAY, NULL);
 	if (ret)
@@ -1511,13 +1521,13 @@ out_free:
 
 int set_memory_array_uc(unsigned long *addr, int addrinarray)
 {
-	return _set_memory_array(addr, addrinarray, _PAGE_CACHE_UC_MINUS);
+	return _set_memory_array(addr, addrinarray, _PAGE_CACHE_MODE_UC_MINUS);
 }
 EXPORT_SYMBOL(set_memory_array_uc);
 
 int set_memory_array_wc(unsigned long *addr, int addrinarray)
 {
-	return _set_memory_array(addr, addrinarray, _PAGE_CACHE_WC);
+	return _set_memory_array(addr, addrinarray, _PAGE_CACHE_MODE_WC);
 }
 EXPORT_SYMBOL(set_memory_array_wc);
 
@@ -1527,10 +1537,12 @@ int _set_memory_wc(unsigned long addr, int numpages)
 	unsigned long addr_copy = addr;
 
 	ret = change_page_attr_set(&addr, numpages,
-				    __pgprot(_PAGE_CACHE_UC_MINUS), 0);
+				   cachemode2pgprot(_PAGE_CACHE_MODE_UC_MINUS),
+				   0);
 	if (!ret) {
 		ret = change_page_attr_set_clr(&addr_copy, numpages,
-					       __pgprot(_PAGE_CACHE_WC),
+					       cachemode2pgprot(
+						   _PAGE_CACHE_MODE_WC),
 					       __pgprot(_PAGE_CACHE_MASK),
 					       0, 0, NULL);
 	}
@@ -1545,7 +1557,7 @@ int set_memory_wc(unsigned long addr, int numpages)
 		return set_memory_uc(addr, numpages);
 
 	ret = reserve_memtype(__pa(addr), __pa(addr) + numpages * PAGE_SIZE,
-		_PAGE_CACHE_WC, NULL);
+		_PAGE_CACHE_MODE_WC, NULL);
 	if (ret)
 		goto out_err;
 
@@ -1564,6 +1576,7 @@ EXPORT_SYMBOL(set_memory_wc);
 
 int _set_memory_wb(unsigned long addr, int numpages)
 {
+	/* WB cache mode is hard wired to all cache attribute bits being 0 */
 	return change_page_attr_clear(&addr, numpages,
 				      __pgprot(_PAGE_CACHE_MASK), 0);
 }
@@ -1586,6 +1599,7 @@ int set_memory_array_wb(unsigned long *addr, int addrinarray)
 	int i;
 	int ret;
 
+	/* WB cache mode is hard wired to all cache attribute bits being 0 */
 	ret = change_page_attr_clear(addr, addrinarray,
 				      __pgprot(_PAGE_CACHE_MASK), 1);
 	if (ret)
@@ -1648,7 +1662,7 @@ int set_pages_uc(struct page *page, int numpages)
 EXPORT_SYMBOL(set_pages_uc);
 
 static int _set_pages_array(struct page **pages, int addrinarray,
-		unsigned long new_type)
+		enum page_cache_mode new_type)
 {
 	unsigned long start;
 	unsigned long end;
@@ -1666,10 +1680,11 @@ static int _set_pages_array(struct page **pages, int addrinarray,
 	}
 
 	ret = cpa_set_pages_array(pages, addrinarray,
-			__pgprot(_PAGE_CACHE_UC_MINUS));
-	if (!ret && new_type == _PAGE_CACHE_WC)
+			cachemode2pgprot(_PAGE_CACHE_MODE_UC_MINUS));
+	if (!ret && new_type == _PAGE_CACHE_MODE_WC)
 		ret = change_page_attr_set_clr(NULL, addrinarray,
-					       __pgprot(_PAGE_CACHE_WC),
+					       cachemode2pgprot(
+						   _PAGE_CACHE_MODE_WC),
 					       __pgprot(_PAGE_CACHE_MASK),
 					       0, CPA_PAGES_ARRAY, pages);
 	if (ret)
@@ -1689,13 +1704,13 @@ err_out:
 
 int set_pages_array_uc(struct page **pages, int addrinarray)
 {
-	return _set_pages_array(pages, addrinarray, _PAGE_CACHE_UC_MINUS);
+	return _set_pages_array(pages, addrinarray, _PAGE_CACHE_MODE_UC_MINUS);
 }
 EXPORT_SYMBOL(set_pages_array_uc);
 
 int set_pages_array_wc(struct page **pages, int addrinarray)
 {
-	return _set_pages_array(pages, addrinarray, _PAGE_CACHE_WC);
+	return _set_pages_array(pages, addrinarray, _PAGE_CACHE_MODE_WC);
 }
 EXPORT_SYMBOL(set_pages_array_wc);
 
@@ -1714,6 +1729,7 @@ int set_pages_array_wb(struct page **pages, int addrinarray)
 	unsigned long end;
 	int i;
 
+	/* WB cache mode is hard wired to all cache attribute bits being 0 */
 	retval = cpa_clear_pages_array(pages, addrinarray,
 			__pgprot(_PAGE_CACHE_MASK));
 	if (retval)
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 6574388..ef75f3f 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -139,20 +139,21 @@ static DEFINE_SPINLOCK(memtype_lock);	/* protects memtype accesses */
  * The intersection is based on "Effective Memory Type" tables in IA-32
  * SDM vol 3a
  */
-static unsigned long pat_x_mtrr_type(u64 start, u64 end, unsigned long req_type)
+static unsigned long pat_x_mtrr_type(u64 start, u64 end,
+				     enum page_cache_mode req_type)
 {
 	/*
 	 * Look for MTRR hint to get the effective type in case where PAT
 	 * request is for WB.
 	 */
-	if (req_type == _PAGE_CACHE_WB) {
+	if (req_type == _PAGE_CACHE_MODE_WB) {
 		u8 mtrr_type;
 
 		mtrr_type = mtrr_type_lookup(start, end);
 		if (mtrr_type != MTRR_TYPE_WRBACK)
-			return _PAGE_CACHE_UC_MINUS;
+			return _PAGE_CACHE_MODE_UC_MINUS;
 
-		return _PAGE_CACHE_WB;
+		return _PAGE_CACHE_MODE_WB;
 	}
 
 	return req_type;
@@ -207,25 +208,26 @@ static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end)
  * - Find the memtype of all the pages in the range, look for any conflicts
  * - In case of no conflicts, set the new memtype for pages in the range
  */
-static int reserve_ram_pages_type(u64 start, u64 end, unsigned long req_type,
-				  unsigned long *new_type)
+static int reserve_ram_pages_type(u64 start, u64 end,
+				  enum page_cache_mode req_type,
+				  enum page_cache_mode *new_type)
 {
 	struct page *page;
 	u64 pfn;
 
-	if (req_type == _PAGE_CACHE_UC) {
+	if (req_type == _PAGE_CACHE_MODE_UC) {
 		/* We do not support strong UC */
 		WARN_ON_ONCE(1);
-		req_type = _PAGE_CACHE_UC_MINUS;
+		req_type = _PAGE_CACHE_MODE_UC_MINUS;
 	}
 
 	for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
-		unsigned long type;
+		enum page_cache_mode type;
 
 		page = pfn_to_page(pfn);
 		type = get_page_memtype(page);
 		if (type != -1) {
-			printk(KERN_INFO "reserve_ram_pages_type failed [mem %#010Lx-%#010Lx], track 0x%lx, req 0x%lx\n",
+			pr_info("reserve_ram_pages_type failed [mem %#010Lx-%#010Lx], track 0x%x, req 0x%x\n",
 				start, end - 1, type, req_type);
 			if (new_type)
 				*new_type = type;
@@ -258,21 +260,21 @@ static int free_ram_pages_type(u64 start, u64 end)
 
 /*
  * req_type typically has one of the:
- * - _PAGE_CACHE_WB
- * - _PAGE_CACHE_WC
- * - _PAGE_CACHE_UC_MINUS
- * - _PAGE_CACHE_UC
+ * - _PAGE_CACHE_MODE_WB
+ * - _PAGE_CACHE_MODE_WC
+ * - _PAGE_CACHE_MODE_UC_MINUS
+ * - _PAGE_CACHE_MODE_UC
  *
  * If new_type is NULL, function will return an error if it cannot reserve the
  * region with req_type. If new_type is non-NULL, function will return
  * available type in new_type in case of no error. In case of any error
  * it will return a negative return value.
  */
-int reserve_memtype(u64 start, u64 end, unsigned long req_type,
-		    unsigned long *new_type)
+int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
+		    enum page_cache_mode *new_type)
 {
 	struct memtype *new;
-	unsigned long actual_type;
+	enum page_cache_mode actual_type;
 	int is_range_ram;
 	int err = 0;
 
@@ -281,10 +283,10 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
 	if (!pat_enabled) {
 		/* This is identical to page table setting without PAT */
 		if (new_type) {
-			if (req_type == _PAGE_CACHE_WC)
-				*new_type = _PAGE_CACHE_UC_MINUS;
+			if (req_type == _PAGE_CACHE_MODE_WC)
+				*new_type = _PAGE_CACHE_MODE_UC_MINUS;
 			else
-				*new_type = req_type & _PAGE_CACHE_MASK;
+				*new_type = req_type;
 		}
 		return 0;
 	}
@@ -292,7 +294,7 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
 	/* Low ISA region is always mapped WB in page table. No need to track */
 	if (x86_platform.is_untracked_pat_range(start, end)) {
 		if (new_type)
-			*new_type = _PAGE_CACHE_WB;
+			*new_type = _PAGE_CACHE_MODE_WB;
 		return 0;
 	}
 
@@ -302,7 +304,7 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
 	 * tools and ACPI tools). Use WB request for WB memory and use
 	 * UC_MINUS otherwise.
 	 */
-	actual_type = pat_x_mtrr_type(start, end, req_type & _PAGE_CACHE_MASK);
+	actual_type = pat_x_mtrr_type(start, end, req_type);
 
 	if (new_type)
 		*new_type = actual_type;
@@ -394,12 +396,12 @@ int free_memtype(u64 start, u64 end)
  *
  * Only to be called when PAT is enabled
  *
- * Returns _PAGE_CACHE_WB, _PAGE_CACHE_WC, _PAGE_CACHE_UC_MINUS or
- * _PAGE_CACHE_UC
+ * Returns _PAGE_CACHE_MODE_WB, _PAGE_CACHE_MODE_WC, _PAGE_CACHE_MODE_UC_MINUS
+ * or _PAGE_CACHE_MODE_UC
  */
-static unsigned long lookup_memtype(u64 paddr)
+static enum page_cache_mode lookup_memtype(u64 paddr)
 {
-	int rettype = _PAGE_CACHE_WB;
+	enum page_cache_mode rettype = _PAGE_CACHE_MODE_WB;
 	struct memtype *entry;
 
 	if (x86_platform.is_untracked_pat_range(paddr, paddr + PAGE_SIZE))
@@ -414,7 +416,7 @@ static unsigned long lookup_memtype(u64 paddr)
 		 * default state and not reserved, and hence of type WB
 		 */
 		if (rettype == -1)
-			rettype = _PAGE_CACHE_WB;
+			rettype = _PAGE_CACHE_MODE_WB;
 
 		return rettype;
 	}
@@ -425,7 +427,7 @@ static unsigned long lookup_memtype(u64 paddr)
 	if (entry != NULL)
 		rettype = entry->type;
 	else
-		rettype = _PAGE_CACHE_UC_MINUS;
+		rettype = _PAGE_CACHE_MODE_UC_MINUS;
 
 	spin_unlock(&memtype_lock);
 	return rettype;
@@ -442,11 +444,11 @@ static unsigned long lookup_memtype(u64 paddr)
  * On failure, returns non-zero
  */
 int io_reserve_memtype(resource_size_t start, resource_size_t end,
-			unsigned long *type)
+			enum page_cache_mode *type)
 {
 	resource_size_t size = end - start;
-	unsigned long req_type = *type;
-	unsigned long new_type;
+	enum page_cache_mode req_type = *type;
+	enum page_cache_mode new_type;
 	int ret;
 
 	WARN_ON_ONCE(iomem_map_sanity_check(start, size));
@@ -520,13 +522,13 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 				unsigned long size, pgprot_t *vma_prot)
 {
-	unsigned long flags = _PAGE_CACHE_WB;
+	enum page_cache_mode pcm = _PAGE_CACHE_MODE_WB;
 
 	if (!range_is_allowed(pfn, size))
 		return 0;
 
 	if (file->f_flags & O_DSYNC)
-		flags = _PAGE_CACHE_UC_MINUS;
+		pcm = _PAGE_CACHE_MODE_UC_MINUS;
 
 #ifdef CONFIG_X86_32
 	/*
@@ -543,12 +545,12 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 	      boot_cpu_has(X86_FEATURE_CYRIX_ARR) ||
 	      boot_cpu_has(X86_FEATURE_CENTAUR_MCR)) &&
 	    (pfn << PAGE_SHIFT) >= __pa(high_memory)) {
-		flags = _PAGE_CACHE_UC;
+		pcm = _PAGE_CACHE_MODE_UC;
 	}
 #endif
 
 	*vma_prot = __pgprot((pgprot_val(*vma_prot) & ~_PAGE_CACHE_MASK) |
-			     flags);
+			     cachemode2protval(pcm));
 	return 1;
 }
 
@@ -556,7 +558,8 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
  * Change the memory type for the physial address range in kernel identity
  * mapping space if that range is a part of identity map.
  */
-int kernel_map_sync_memtype(u64 base, unsigned long size, unsigned long flags)
+int kernel_map_sync_memtype(u64 base, unsigned long size,
+			    enum page_cache_mode pcm)
 {
 	unsigned long id_sz;
 
@@ -574,11 +577,11 @@ int kernel_map_sync_memtype(u64 base, unsigned long size, unsigned long flags)
 				__pa(high_memory) - base :
 				size;
 
-	if (ioremap_change_attr((unsigned long)__va(base), id_sz, flags) < 0) {
+	if (ioremap_change_attr((unsigned long)__va(base), id_sz, pcm) < 0) {
 		printk(KERN_INFO "%s:%d ioremap_change_attr failed %s "
 			"for [mem %#010Lx-%#010Lx]\n",
 			current->comm, current->pid,
-			cattr_name(flags),
+			cattr_name(pcm),
 			base, (unsigned long long)(base + size-1));
 		return -EINVAL;
 	}
@@ -595,8 +598,8 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
 {
 	int is_ram = 0;
 	int ret;
-	unsigned long want_flags = (pgprot_val(*vma_prot) & _PAGE_CACHE_MASK);
-	unsigned long flags = want_flags;
+	enum page_cache_mode want_pcm = pgprot2cachemode(*vma_prot);
+	enum page_cache_mode pcm = want_pcm;
 
 	is_ram = pat_pagerange_is_ram(paddr, paddr + size);
 
@@ -609,36 +612,36 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
 		if (!pat_enabled)
 			return 0;
 
-		flags = lookup_memtype(paddr);
-		if (want_flags != flags) {
+		pcm = lookup_memtype(paddr);
+		if (want_pcm != pcm) {
 			printk(KERN_WARNING "%s:%d map pfn RAM range req %s for [mem %#010Lx-%#010Lx], got %s\n",
 				current->comm, current->pid,
-				cattr_name(want_flags),
+				cattr_name(want_pcm),
 				(unsigned long long)paddr,
 				(unsigned long long)(paddr + size - 1),
-				cattr_name(flags));
+				cattr_name(pcm));
 			*vma_prot = __pgprot((pgprot_val(*vma_prot) &
-					      (~_PAGE_CACHE_MASK)) |
-					     flags);
+					     (~_PAGE_CACHE_MASK)) |
+					     cachemode2protval(pcm));
 		}
 		return 0;
 	}
 
-	ret = reserve_memtype(paddr, paddr + size, want_flags, &flags);
+	ret = reserve_memtype(paddr, paddr + size, want_pcm, &pcm);
 	if (ret)
 		return ret;
 
-	if (flags != want_flags) {
+	if (pcm != want_pcm) {
 		if (strict_prot ||
-		    !is_new_memtype_allowed(paddr, size, want_flags, flags)) {
+		    !is_new_memtype_allowed(paddr, size, want_pcm, pcm)) {
 			free_memtype(paddr, paddr + size);
 			printk(KERN_ERR "%s:%d map pfn expected mapping type %s"
 				" for [mem %#010Lx-%#010Lx], got %s\n",
 				current->comm, current->pid,
-				cattr_name(want_flags),
+				cattr_name(want_pcm),
 				(unsigned long long)paddr,
 				(unsigned long long)(paddr + size - 1),
-				cattr_name(flags));
+				cattr_name(pcm));
 			return -EINVAL;
 		}
 		/*
@@ -647,10 +650,10 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
 		 */
 		*vma_prot = __pgprot((pgprot_val(*vma_prot) &
 				      (~_PAGE_CACHE_MASK)) |
-				     flags);
+				     cachemode2protval(pcm));
 	}
 
-	if (kernel_map_sync_memtype(paddr, size, flags) < 0) {
+	if (kernel_map_sync_memtype(paddr, size, pcm) < 0) {
 		free_memtype(paddr, paddr + size);
 		return -EINVAL;
 	}
@@ -709,7 +712,7 @@ int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 		    unsigned long pfn, unsigned long addr, unsigned long size)
 {
 	resource_size_t paddr = (resource_size_t)pfn << PAGE_SHIFT;
-	unsigned long flags;
+	enum page_cache_mode pcm;
 
 	/* reserve the whole chunk starting from paddr */
 	if (addr == vma->vm_start && size == (vma->vm_end - vma->vm_start)) {
@@ -728,18 +731,18 @@ int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 	 * For anything smaller than the vma size we set prot based on the
 	 * lookup.
 	 */
-	flags = lookup_memtype(paddr);
+	pcm = lookup_memtype(paddr);
 
 	/* Check memtype for the remaining pages */
 	while (size > PAGE_SIZE) {
 		size -= PAGE_SIZE;
 		paddr += PAGE_SIZE;
-		if (flags != lookup_memtype(paddr))
+		if (pcm != lookup_memtype(paddr))
 			return -EINVAL;
 	}
 
 	*prot = __pgprot((pgprot_val(vma->vm_page_prot) & (~_PAGE_CACHE_MASK)) |
-			 flags);
+			 cachemode2protval(pcm));
 
 	return 0;
 }
@@ -747,15 +750,15 @@ int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 int track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
 		     unsigned long pfn)
 {
-	unsigned long flags;
+	enum page_cache_mode pcm;
 
 	if (!pat_enabled)
 		return 0;
 
 	/* Set prot based on lookup */
-	flags = lookup_memtype((resource_size_t)pfn << PAGE_SHIFT);
+	pcm = lookup_memtype((resource_size_t)pfn << PAGE_SHIFT);
 	*prot = __pgprot((pgprot_val(vma->vm_page_prot) & (~_PAGE_CACHE_MASK)) |
-			 flags);
+			 cachemode2protval(pcm));
 
 	return 0;
 }
@@ -791,7 +794,8 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
 pgprot_t pgprot_writecombine(pgprot_t prot)
 {
 	if (pat_enabled)
-		return __pgprot(pgprot_val(prot) | _PAGE_CACHE_WC);
+		return __pgprot(pgprot_val(prot) |
+				cachemode2protval(_PAGE_CACHE_MODE_WC));
 	else
 		return pgprot_noncached(prot);
 }
diff --git a/arch/x86/mm/pat_internal.h b/arch/x86/mm/pat_internal.h
index 77e5ba1..f641162 100644
--- a/arch/x86/mm/pat_internal.h
+++ b/arch/x86/mm/pat_internal.h
@@ -10,30 +10,32 @@ struct memtype {
 	u64			start;
 	u64			end;
 	u64			subtree_max_end;
-	unsigned long		type;
+	enum page_cache_mode	type;
 	struct rb_node		rb;
 };
 
-static inline char *cattr_name(unsigned long flags)
+static inline char *cattr_name(enum page_cache_mode pcm)
 {
-	switch (flags & _PAGE_CACHE_MASK) {
-	case _PAGE_CACHE_UC:		return "uncached";
-	case _PAGE_CACHE_UC_MINUS:	return "uncached-minus";
-	case _PAGE_CACHE_WB:		return "write-back";
-	case _PAGE_CACHE_WC:		return "write-combining";
-	default:			return "broken";
+	switch (pcm) {
+	case _PAGE_CACHE_MODE_UC:		return "uncached";
+	case _PAGE_CACHE_MODE_UC_MINUS:		return "uncached-minus";
+	case _PAGE_CACHE_MODE_WB:		return "write-back";
+	case _PAGE_CACHE_MODE_WC:		return "write-combining";
+	case _PAGE_CACHE_MODE_WT:		return "write-through";
+	case _PAGE_CACHE_MODE_WP:		return "write-protected";
+	default:				return "broken";
 	}
 }
 
 #ifdef CONFIG_X86_PAT
 extern int rbt_memtype_check_insert(struct memtype *new,
-					unsigned long *new_type);
+					enum page_cache_mode *new_type);
 extern struct memtype *rbt_memtype_erase(u64 start, u64 end);
 extern struct memtype *rbt_memtype_lookup(u64 addr);
 extern int rbt_memtype_copy_nth_element(struct memtype *out, loff_t pos);
 #else
 static inline int rbt_memtype_check_insert(struct memtype *new,
-					unsigned long *new_type)
+					enum page_cache_mode *new_type)
 { return 0; }
 static inline struct memtype *rbt_memtype_erase(u64 start, u64 end)
 { return NULL; }
diff --git a/arch/x86/mm/pat_rbtree.c b/arch/x86/mm/pat_rbtree.c
index 415f6c4..6582adc 100644
--- a/arch/x86/mm/pat_rbtree.c
+++ b/arch/x86/mm/pat_rbtree.c
@@ -122,11 +122,12 @@ static struct memtype *memtype_rb_exact_match(struct rb_root *root,
 
 static int memtype_rb_check_conflict(struct rb_root *root,
 				u64 start, u64 end,
-				unsigned long reqtype, unsigned long *newtype)
+				enum page_cache_mode reqtype,
+				enum page_cache_mode *newtype)
 {
 	struct rb_node *node;
 	struct memtype *match;
-	int found_type = reqtype;
+	enum page_cache_mode found_type = reqtype;
 
 	match = memtype_rb_lowest_match(&memtype_rbroot, start, end);
 	if (match == NULL)
@@ -187,7 +188,8 @@ static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
 	rb_insert_augmented(&newdata->rb, root, &memtype_rb_augment_cb);
 }
 
-int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
+int rbt_memtype_check_insert(struct memtype *new,
+			     enum page_cache_mode *ret_type)
 {
 	int err = 0;
 
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 2ae525e..9d6c9d3 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -433,14 +433,14 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
 		return -EINVAL;
 
 	if (pat_enabled && write_combine)
-		prot |= _PAGE_CACHE_WC;
+		prot |= cachemode2protval(_PAGE_CACHE_MODE_WC);
 	else if (pat_enabled || boot_cpu_data.x86 > 3)
 		/*
 		 * ioremap() and ioremap_nocache() defaults to UC MINUS for now.
 		 * To avoid attribute conflicts, request UC MINUS here
 		 * as well.
 		 */
-		prot |= _PAGE_CACHE_UC_MINUS;
+		prot |= cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS);
 
 	prot |= _PAGE_IOMAP;	/* creating a mapping for IO */
 
diff --git a/drivers/video/fbdev/gbefb.c b/drivers/video/fbdev/gbefb.c
index 4aa56ba..b1cc7a6 100644
--- a/drivers/video/fbdev/gbefb.c
+++ b/drivers/video/fbdev/gbefb.c
@@ -54,7 +54,8 @@ struct gbefb_par {
 #endif
 #endif
 #ifdef CONFIG_X86
-#define pgprot_fb(_prot) ((_prot) | _PAGE_PCD)
+#define pgprot_fb(_prot) (((_prot) & ~_PAGE_CACHE_MASK) |	\
+			  cachemode2protval(_PAGE_CACHE_MODE_UC))
 #endif
 
 /*
diff --git a/drivers/video/fbdev/vermilion/vermilion.c b/drivers/video/fbdev/vermilion/vermilion.c
index 048a666..6bbc559 100644
--- a/drivers/video/fbdev/vermilion/vermilion.c
+++ b/drivers/video/fbdev/vermilion/vermilion.c
@@ -1004,13 +1004,15 @@ static int vmlfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	struct vml_info *vinfo = container_of(info, struct vml_info, info);
 	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
 	int ret;
+	unsigned long prot;
 
 	ret = vmlfb_vram_offset(vinfo, offset);
 	if (ret)
 		return -EINVAL;
 
-	pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
-	pgprot_val(vma->vm_page_prot) &= ~_PAGE_PWT;
+	prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
+	pgprot_val(vma->vm_page_prot) =
+		prot | cachemode2protval(_PAGE_CACHE_MODE_UC);
 
 	return vm_iomap_memory(vma, vinfo->vram_start,
 			vinfo->vram_contig_size);
-- 
1.8.4.5

Re: [PATCH 1/3] x86: Make page cache mode a real type

[Toshi Kani]

On Tue, 2014-08-26 at 08:16 +0200, Juergen Gross wrote:
> At the moment there are a lot of places that handle setting or getting
> the page cache mode by treating the pgprot bits equal to the cache mode.
> This is only true because there are a lot of assumptions about the setup
> of the PAT MSR. Otherwise the cache type needs to get translated into
> pgprot bits and vice versa.
> 
> This patch tries to prepare for that by introducing a seperate type
> for the cache mode and adding functions to translate between those and pgprot
> values.
> 
> To avoid too much performance penalty the translation between cache mode
> and pgprot values is done via tables which contain the relevant information.
> Write-back cache mode is hard-wired to be 0, all other modes are configurable
> via those tables. For large pages there are translation functions as the
> PAT bit is located at different positions in the ptes of 4k and large pages.
> 
> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Hi Juergen,

Thanks for the updates!  A few comments below...

> @@ -73,6 +73,9 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>  /*
>   * Map 'pfn' using protections 'prot'
>   */
> +#define __PAGE_KERNEL_WC	(__PAGE_KERNEL | \
> +				 cachemode2protval(_PAGE_CACHE_MODE_WC))
> +
>  void __iomem *
>  iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>  {
> @@ -82,12 +85,14 @@ iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>  	 * MTRR is UC or WC.  UC_MINUS gets the real intention, of the
>  	 * user, which is "WC if the MTRR is WC, UC if you can't do that."
>  	 */
> -	if (!pat_enabled && pgprot_val(prot) == pgprot_val(PAGE_KERNEL_WC))
> -		prot = PAGE_KERNEL_UC_MINUS;
> +	if (!pat_enabled && pgprot_val(prot) == __PAGE_KERNEL_WC)
> +		prot = __pgprot(__PAGE_KERNEL |
> +				protval_pagemode(_PAGE_CACHE_MODE_UC_MINUS));

protval_pagemode() should be cachemode2protval().
 
>  /*
> diff --git a/drivers/video/fbdev/vermilion/vermilion.c b/drivers/video/fbdev/vermilion/vermilion.c
> index 048a666..6bbc559 100644
> --- a/drivers/video/fbdev/vermilion/vermilion.c
> +++ b/drivers/video/fbdev/vermilion/vermilion.c
> @@ -1004,13 +1004,15 @@ static int vmlfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
>  	struct vml_info *vinfo = container_of(info, struct vml_info, info);
>  	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
>  	int ret;
> +	unsigned long prot;
>  
>  	ret = vmlfb_vram_offset(vinfo, offset);
>  	if (ret)
>  		return -EINVAL;
>  
> -	pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
> -	pgprot_val(vma->vm_page_prot) &= ~_PAGE_PWT;
> +	prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
> +	pgprot_val(vma->vm_page_prot) =
> +		prot | cachemode2protval(_PAGE_CACHE_MODE_UC);

This cache mode should be _PAGE_CACHE_MODE_UC_MINUS as the original code
only sets the PCD bit.

Thanks,
-Toshi

Re: [Xen-devel] [PATCH 1/3] x86: Make page cache mode a real type

[Juergen Gross]

On 08/26/2014 09:44 PM, Toshi Kani wrote:
> On Tue, 2014-08-26 at 08:16 +0200, Juergen Gross wrote:
>> At the moment there are a lot of places that handle setting or getting
>> the page cache mode by treating the pgprot bits equal to the cache mode.
>> This is only true because there are a lot of assumptions about the setup
>> of the PAT MSR. Otherwise the cache type needs to get translated into
>> pgprot bits and vice versa.
>>
>> This patch tries to prepare for that by introducing a seperate type
>> for the cache mode and adding functions to translate between those and pgprot
>> values.
>>
>> To avoid too much performance penalty the translation between cache mode
>> and pgprot values is done via tables which contain the relevant information.
>> Write-back cache mode is hard-wired to be 0, all other modes are configurable
>> via those tables. For large pages there are translation functions as the
>> PAT bit is located at different positions in the ptes of 4k and large pages.
>>
>> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>
> Hi Juergen,
>
> Thanks for the updates!  A few comments below...
>
>> @@ -73,6 +73,9 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>>   /*
>>    * Map 'pfn' using protections 'prot'
>>    */
>> +#define __PAGE_KERNEL_WC	(__PAGE_KERNEL | \
>> +				 cachemode2protval(_PAGE_CACHE_MODE_WC))
>> +
>>   void __iomem *
>>   iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>>   {
>> @@ -82,12 +85,14 @@ iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>>   	 * MTRR is UC or WC.  UC_MINUS gets the real intention, of the
>>   	 * user, which is "WC if the MTRR is WC, UC if you can't do that."
>>   	 */
>> -	if (!pat_enabled && pgprot_val(prot) == pgprot_val(PAGE_KERNEL_WC))
>> -		prot = PAGE_KERNEL_UC_MINUS;
>> +	if (!pat_enabled && pgprot_val(prot) == __PAGE_KERNEL_WC)
>> +		prot = __pgprot(__PAGE_KERNEL |
>> +				protval_pagemode(_PAGE_CACHE_MODE_UC_MINUS));
>
> protval_pagemode() should be cachemode2protval().

Obviously, yes.

>
>>   /*
>> diff --git a/drivers/video/fbdev/vermilion/vermilion.c b/drivers/video/fbdev/vermilion/vermilion.c
>> index 048a666..6bbc559 100644
>> --- a/drivers/video/fbdev/vermilion/vermilion.c
>> +++ b/drivers/video/fbdev/vermilion/vermilion.c
>> @@ -1004,13 +1004,15 @@ static int vmlfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
>>   	struct vml_info *vinfo = container_of(info, struct vml_info, info);
>>   	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
>>   	int ret;
>> +	unsigned long prot;
>>
>>   	ret = vmlfb_vram_offset(vinfo, offset);
>>   	if (ret)
>>   		return -EINVAL;
>>
>> -	pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
>> -	pgprot_val(vma->vm_page_prot) &= ~_PAGE_PWT;
>> +	prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
>> +	pgprot_val(vma->vm_page_prot) =
>> +		prot | cachemode2protval(_PAGE_CACHE_MODE_UC);
>
> This cache mode should be _PAGE_CACHE_MODE_UC_MINUS as the original code
> only sets the PCD bit.

I'll change it.

Thanks,

Juergen

[PATCH 2/3] x86: Enable PAT to use cache mode translation tables

[Juergen Gross]

Update the translation tables from cache mode to pgprot values according to
the PAT settings. This enables changing the cache attributes of a PAT index in
just one place without having to change at the users side.

With this change it is possible to use the same kernel with different PAT
configurations, e.g. supporting Xen.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/include/asm/pat.h           |  1 +
 arch/x86/include/asm/pgtable_types.h |  4 +++
 arch/x86/mm/init.c                   |  8 ++++++
 arch/x86/mm/pat.c                    | 54 ++++++++++++++++++++++++++++++++++--
 include/linux/mm.h                   |  1 +
 5 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index 150407a..91bc4ba 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -11,6 +11,7 @@ static const int pat_enabled;
 #endif
 
 extern void pat_init(void);
+void pat_init_cache_modes(void);
 
 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/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 0d38511..bd2f50f 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -338,6 +338,10 @@ extern uint8_t __pte2cachemode_tbl[8];
 	((((cb) >> (_PAGE_BIT_PAT - 2)) & 4) |		\
 	 (((cb) >> (_PAGE_BIT_PCD - 1)) & 2) |		\
 	 (((cb) >> _PAGE_BIT_PWT) & 1))
+#define __cm_idx2pte(i)					\
+	((((i) & 4) << (_PAGE_BIT_PAT - 2)) |		\
+	 (((i) & 2) << (_PAGE_BIT_PCD - 1)) |		\
+	 (((i) & 1) << _PAGE_BIT_PWT))
 
 static inline unsigned long cachemode2protval(enum page_cache_mode pcm)
 {
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index a9776ba..82b41d5 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -716,3 +716,11 @@ void __init zone_sizes_init(void)
 	free_area_init_nodes(max_zone_pfns);
 }
 
+void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache)
+{
+	/* entry 0 MUST be WB (hardwired to speed up translations) */
+	BUG_ON(!entry && cache != _PAGE_CACHE_MODE_WB);
+
+	__cachemode2pte_tbl[cache] = __cm_idx2pte(entry);
+	__pte2cachemode_tbl[entry] = cache;
+}
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index ef75f3f..feb4d30 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -75,6 +75,57 @@ enum {
 	PAT_UC_MINUS = 7,	/* UC, but can be overriden by MTRR */
 };
 
+/*
+ * Update the cache mode to pgprot translation tables according to PAT
+ * configuration.
+ * Using lower indices is preferred, so we start with highest index.
+ */
+void pat_init_cache_modes(void)
+{
+	int i;
+	enum page_cache_mode cache;
+	char pat_msg[33];
+	char *cache_mode;
+	u64 pat;
+
+	rdmsrl(MSR_IA32_CR_PAT, pat);
+	pat_msg[32] = 0;
+	for (i = 7; i >= 0; i--) {
+		switch ((pat >> (i * 8)) & 7) {
+		case PAT_UC:
+			cache = _PAGE_CACHE_MODE_UC;
+			cache_mode = "UC  ";
+			break;
+		case PAT_WC:
+			cache = _PAGE_CACHE_MODE_WC;
+			cache_mode = "WC  ";
+			break;
+		case PAT_WT:
+			cache = _PAGE_CACHE_MODE_WT;
+			cache_mode = "WT  ";
+			break;
+		case PAT_WP:
+			cache = _PAGE_CACHE_MODE_WP;
+			cache_mode = "WP  ";
+			break;
+		case PAT_WB:
+			cache = _PAGE_CACHE_MODE_WB;
+			cache_mode = "WB  ";
+			break;
+		case PAT_UC_MINUS:
+			cache = _PAGE_CACHE_MODE_UC_MINUS;
+			cache_mode = "UC- ";
+			break;
+		default:
+			cache = _PAGE_CACHE_MODE_WB;
+			cache_mode = "WB  ";
+		}
+		update_cache_mode_entry(i, cache);
+		memcpy(pat_msg + 4 * i, cache_mode, 4);
+	}
+	pr_info("PAT configuration [0-7]: %s\n", pat_msg);
+}
+
 #define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
 
 void pat_init(void)
@@ -124,8 +175,7 @@ void pat_init(void)
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 
 	if (boot_cpu)
-		printk(KERN_INFO "x86 PAT enabled: cpu %d, old 0x%Lx, new 0x%Lx\n",
-		       smp_processor_id(), boot_pat_state, pat);
+		pat_init_cache_modes();
 }
 
 #undef PAT
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8981cc8..d7bf551 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1574,6 +1574,7 @@ extern void free_area_init(unsigned long * zones_size);
 extern void free_area_init_node(int nid, unsigned long * zones_size,
 		unsigned long zone_start_pfn, unsigned long *zholes_size);
 extern void free_initmem(void);
+extern void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
 
 /*
  * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
-- 
1.8.4.5

Re: [PATCH 2/3] x86: Enable PAT to use cache mode translation tables

[Toshi Kani]

On Tue, 2014-08-26 at 08:16 +0200, Juergen Gross wrote:
> Update the translation tables from cache mode to pgprot values according to
> the PAT settings. This enables changing the cache attributes of a PAT index in
> just one place without having to change at the users side.
> 
> With this change it is possible to use the same kernel with different PAT
> configurations, e.g. supporting Xen.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Toshi Kani <toshi.kani@hp.com>

Thanks,
-Toshi

Re: [PATCH 2/3] x86: Enable PAT to use cache mode translation tables

[Toshi Kani]

On Tue, 2014-08-26 at 08:16 +0200, Juergen Gross wrote:
> Update the translation tables from cache mode to pgprot values according to
> the PAT settings. This enables changing the cache attributes of a PAT index in
> just one place without having to change at the users side.
> 
> With this change it is possible to use the same kernel with different PAT
> configurations, e.g. supporting Xen.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

I know I sent my review-by before, but my build test failed...

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8981cc8..d7bf551 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1574,6 +1574,7 @@ extern void free_area_init(unsigned long * zones_size);
>  extern void free_area_init_node(int nid, unsigned long * zones_size,
>  		unsigned long zone_start_pfn, unsigned long *zholes_size);
>  extern void free_initmem(void);
> +extern void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);

This new interface cannot be defined in this common header file since
page_cache_mode is only defined in x86.  It should be defined in x86
header, such as pat.h.

Thanks,
-Toshi

Re: [PATCH 2/3] x86: Enable PAT to use cache mode translation tables

[Juergen Gross]

On 08/29/2014 01:21 AM, Toshi Kani wrote:
> On Tue, 2014-08-26 at 08:16 +0200, Juergen Gross wrote:
>> Update the translation tables from cache mode to pgprot values according to
>> the PAT settings. This enables changing the cache attributes of a PAT index in
>> just one place without having to change at the users side.
>>
>> With this change it is possible to use the same kernel with different PAT
>> configurations, e.g. supporting Xen.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>
> I know I sent my review-by before, but my build test failed...
>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 8981cc8..d7bf551 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1574,6 +1574,7 @@ extern void free_area_init(unsigned long * zones_size);
>>   extern void free_area_init_node(int nid, unsigned long * zones_size,
>>   		unsigned long zone_start_pfn, unsigned long *zholes_size);
>>   extern void free_initmem(void);
>> +extern void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
>
> This new interface cannot be defined in this common header file since
> page_cache_mode is only defined in x86.  It should be defined in x86
> header, such as pat.h.

Oh, right you are.

Thanks,

Juergen

[PATCH 3/3] Support Xen pv-domains using PAT

[Juergen Gross]

With the dynamical mapping between cache modes and pgprot values it is now
possible to use all cache modes via the Xen hypervisor PAT settings in a
pv domain.

All to be done is to read the PAT configuration MSR and set up the translation
tables accordingly.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/enlighten.c | 11 ++++++----
 arch/x86/xen/mmu.c       | 52 ++++++++++++------------------------------------
 arch/x86/xen/xen-ops.h   |  1 +
 3 files changed, 21 insertions(+), 43 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c0cb11f..113c01c 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1552,12 +1552,15 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
 	xen_init_mmu_ops();
 
+	/*
+	 * Modify the cache mode translation tables to match Xen's PAT
+	 * configuration.
+	 */
+
+	xen_init_cache_types();
+
 	/* Prevent unwanted bits from being set in PTEs. */
 	__supported_pte_mask &= ~_PAGE_GLOBAL;
-#if 0
-	if (!xen_initial_domain())
-#endif
-		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
 
 	__supported_pte_mask |= _PAGE_IOMAP;
 
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index e8a1201..4d1c736 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -434,13 +434,7 @@ static pteval_t iomap_pte(pteval_t val)
 __visible pteval_t xen_pte_val(pte_t pte)
 {
 	pteval_t pteval = pte.pte;
-#if 0
-	/* If this is a WC pte, convert back from Xen WC to Linux WC */
-	if ((pteval & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)) == _PAGE_PAT) {
-		WARN_ON(!pat_enabled);
-		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
-	}
-#endif
+
 	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
 		return pteval;
 
@@ -455,47 +449,27 @@ __visible pgdval_t xen_pgd_val(pgd_t pgd)
 PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);
 
 /*
- * Xen's PAT setup is part of its ABI, though I assume entries 6 & 7
- * are reserved for now, to correspond to the Intel-reserved PAT
- * types.
- *
- * We expect Linux's PAT set as follows:
- *
- * Idx  PTE flags        Linux    Xen    Default
- * 0                     WB       WB     WB
- * 1            PWT      WC       WT     WT
- * 2        PCD          UC-      UC-    UC-
- * 3        PCD PWT      UC       UC     UC
- * 4    PAT              WB       WC     WB
- * 5    PAT     PWT      WC       WP     WT
- * 6    PAT PCD          UC-      rsv    UC-
- * 7    PAT PCD PWT      UC       rsv    UC
+ * Xen's PAT setup is part of its ABI.
+ * We don't care what Linux wants to use, just fall back to the Xen PAT
+ * configuration. All we have to do in case of a Linux's PAT configuration
+ * is to overwrite the cache mode translation tables with the correct
+ * values for the Xen configuration.
  */
 
+void xen_init_cache_types(void)
+{
+	pat_init_cache_modes();
+}
+
 void xen_set_pat(u64 pat)
 {
-	/* We expect Linux to use a PAT setting of
-	 * UC UC- WC WB (ignoring the PAT flag) */
-	WARN_ON(pat != 0x0007010600070106ull);
+	xen_init_cache_types();
 }
 
 __visible pte_t xen_make_pte(pteval_t pte)
 {
 	phys_addr_t addr = (pte & PTE_PFN_MASK);
-#if 0
-	/* If Linux is trying to set a WC pte, then map to the Xen WC.
-	 * If _PAGE_PAT is set, then it probably means it is really
-	 * _PAGE_PSE, so avoid fiddling with the PAT mapping and hope
-	 * things work out OK...
-	 *
-	 * (We should never see kernel mappings with _PAGE_PSE set,
-	 * but we could see hugetlbfs mappings, I think.).
-	 */
-	if (pat_enabled && !WARN_ON(pte & _PAGE_PAT)) {
-		if ((pte & (_PAGE_PCD | _PAGE_PWT)) == _PAGE_PWT)
-			pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
-	}
-#endif
+
 	/*
 	 * Unprivileged domains are allowed to do IOMAPpings for
 	 * PCI passthrough, but not map ISA space.  The ISA
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 28c7e0b..348e68aa 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -34,6 +34,7 @@ extern unsigned long xen_max_p2m_pfn;
 void xen_mm_pin_all(void);
 void xen_mm_unpin_all(void);
 void xen_set_pat(u64);
+void xen_init_cache_types(void);
 
 char * __init xen_memory_setup(void);
 char * xen_auto_xlated_memory_setup(void);
-- 
1.8.4.5

Re: [Xen-devel] [PATCH 3/3] Support Xen pv-domains using PAT

[David Vrabel]

On 26/08/14 07:16, Juergen Gross wrote:
> With the dynamical mapping between cache modes and pgprot values it is now
> possible to use all cache modes via the Xen hypervisor PAT settings in a
> pv domain.
> 
> All to be done is to read the PAT configuration MSR and set up the translation
> tables accordingly.
[...]
> +void xen_init_cache_types(void)
> +{
> +	pat_init_cache_modes();
> +}

No need to introduce xen_init_cache_types(), just call
pat_init_cache_modes() directly.

>  void xen_set_pat(u64 pat)
>  {
> -	/* We expect Linux to use a PAT setting of
> -	 * UC UC- WC WB (ignoring the PAT flag) */
> -	WARN_ON(pat != 0x0007010600070106ull);
> +	xen_init_cache_types();
>  }

Remove xen_set_pat() and remove the special-cased handling of the PAT
MSR from xen_write_msr_safe().

David

Re: [Xen-devel] [PATCH 3/3] Support Xen pv-domains using PAT

[David Vrabel]

On 26/08/14 07:16, Juergen Gross wrote:
> With the dynamical mapping between cache modes and pgprot values it is now
> possible to use all cache modes via the Xen hypervisor PAT settings in a
> pv domain.
> 
> All to be done is to read the PAT configuration MSR and set up the translation
> tables accordingly.
[...]
> +void xen_init_cache_types(void)
> +{
> +	pat_init_cache_modes();
> +}

No need to introduce xen_init_cache_types(), just call
pat_init_cache_modes() directly.

>  void xen_set_pat(u64 pat)
>  {
> -	/* We expect Linux to use a PAT setting of
> -	 * UC UC- WC WB (ignoring the PAT flag) */
> -	WARN_ON(pat != 0x0007010600070106ull);
> +	xen_init_cache_types();
>  }

Remove xen_set_pat() and remove the special-cased handling of the PAT
MSR from xen_write_msr_safe().

David

Re: [Xen-devel] [PATCH 3/3] Support Xen pv-domains using PAT

[Juergen Gross]

On 08/26/2014 12:59 PM, David Vrabel wrote:
> On 26/08/14 07:16, Juergen Gross wrote:
>> With the dynamical mapping between cache modes and pgprot values it is now
>> possible to use all cache modes via the Xen hypervisor PAT settings in a
>> pv domain.
>>
>> All to be done is to read the PAT configuration MSR and set up the translation
>> tables accordingly.
> [...]
>> +void xen_init_cache_types(void)
>> +{
>> +	pat_init_cache_modes();
>> +}
>
> No need to introduce xen_init_cache_types(), just call
> pat_init_cache_modes() directly.

Indeed. This was a leftover from a previous version.

>
>>   void xen_set_pat(u64 pat)
>>   {
>> -	/* We expect Linux to use a PAT setting of
>> -	 * UC UC- WC WB (ignoring the PAT flag) */
>> -	WARN_ON(pat != 0x0007010600070106ull);
>> +	xen_init_cache_types();
>>   }
>
> Remove xen_set_pat() and remove the special-cased handling of the PAT
> MSR from xen_write_msr_safe().

Hmm, why not. Reduces Xen specific handling even more.


Juergen

Re: [PATCH 0/3] x86: Full support of PAT

[Andy Lutomirski]

On 08/25/2014 11:16 PM, Juergen Gross wrote:
> The x86 architecture offers via the PAT (Page Attribute Table) a way to
> specify different caching modes in page table entries. The PAT MSR contains
> 8 entries each specifying one of 6 possible cache modes. A pte references one
> of those entries via 3 bits: _PAGE_PAT, _PAGE_PWT and _PAGE_PCD.
> 
> The Linux kernel currently supports only 4 different cache modes. The PAT MSR
> is set up in a way that the setting of _PAGE_PAT in a pte doesn't matter: the
> top 4 entries in the PAT MSR are the same as the 4 lower entries.
> 
> This results in the kernel not supporting e.g. write-through mode. Especially
> this cache mode would speed up drivers of video cards which now have to use
> uncached accesses.
> 
> OTOH some old processors (Pentium) don't support PAT correctly and the Xen
> hypervisor has been using a different PAT MSR configuration for some time now
> and can't change that as this setting is part of the ABI.
> 
> This patch set abstracts the cache mode from the pte and introduces tables to
> translate between cache mode and pte bits (the default cache mode "write back"
> is hard-wired to PAT entry 0). The tables are statically initialized with
> values being compatible to old processors and current usage. As soon as the
> PAT MSR is changed (or - in case of Xen - is read at boot time) the tables are
> changed accordingly. Requests of mappings with special cache modes are always
> possible now, in case they are not supported there will be a fallback to a
> compatible but slower mode.

I feel like I'm missing something here.  Where's the support for the
high PAT bit on huge pages?  Once you start using the top four entries,
you'll need that.

Also, this probably needs errata handling.  IIRC there are a handful of
CPUs that support PAT but don't work correctly if the high bit is set.

--Andy

Re: [PATCH 0/3] x86: Full support of PAT

[Toshi Kani]

On Tue, 2014-08-26 at 11:48 -0700, Andy Lutomirski wrote:
> On 08/25/2014 11:16 PM, Juergen Gross wrote:
> > The x86 architecture offers via the PAT (Page Attribute Table) a way to
> > specify different caching modes in page table entries. The PAT MSR contains
> > 8 entries each specifying one of 6 possible cache modes. A pte references one
> > of those entries via 3 bits: _PAGE_PAT, _PAGE_PWT and _PAGE_PCD.
> > 
> > The Linux kernel currently supports only 4 different cache modes. The PAT MSR
> > is set up in a way that the setting of _PAGE_PAT in a pte doesn't matter: the
> > top 4 entries in the PAT MSR are the same as the 4 lower entries.
> > 
> > This results in the kernel not supporting e.g. write-through mode. Especially
> > this cache mode would speed up drivers of video cards which now have to use
> > uncached accesses.
> > 
> > OTOH some old processors (Pentium) don't support PAT correctly and the Xen
> > hypervisor has been using a different PAT MSR configuration for some time now
> > and can't change that as this setting is part of the ABI.
> > 
> > This patch set abstracts the cache mode from the pte and introduces tables to
> > translate between cache mode and pte bits (the default cache mode "write back"
> > is hard-wired to PAT entry 0). The tables are statically initialized with
> > values being compatible to old processors and current usage. As soon as the
> > PAT MSR is changed (or - in case of Xen - is read at boot time) the tables are
> > changed accordingly. Requests of mappings with special cache modes are always
> > possible now, in case they are not supported there will be a fallback to a
> > compatible but slower mode.
> 
> I feel like I'm missing something here.  Where's the support for the
> high PAT bit on huge pages?  Once you start using the top four entries,
> you'll need that.

pgprot_4k_2_large() and pgprot_large_2_4k() provide the conversion of
the PAT bit.

> Also, this probably needs errata handling.  IIRC there are a handful of
> CPUs that support PAT but don't work correctly if the high bit is set.

This patchset provides the infrastructure, but does not actually use the
upper four entries.  I am working on additional patchset on top of this,
which enables WT with the PAT bit except on the following Intel
processors.  If I missed some processors affected, please let me know.

  errata           cpuid
  --------------------------------------
  Pentium 2, A52   family 0x6, model 0x5
  Pentium 3, E27   family 0x6, model 0x7
  Pentium M, Y26   family 0x6, model 0x9
  Pentium 4, N46   family 0xf, model 0x0

Thanks,
-Toshi

Re: [PATCH 0/3] x86: Full support of PAT

[Andy Lutomirski]

On Tue, Aug 26, 2014 at 1:08 PM, Toshi Kani <toshi.kani@hp.com> wrote:
> On Tue, 2014-08-26 at 11:48 -0700, Andy Lutomirski wrote:
>> On 08/25/2014 11:16 PM, Juergen Gross wrote:
>> > The x86 architecture offers via the PAT (Page Attribute Table) a way to
>> > specify different caching modes in page table entries. The PAT MSR contains
>> > 8 entries each specifying one of 6 possible cache modes. A pte references one
>> > of those entries via 3 bits: _PAGE_PAT, _PAGE_PWT and _PAGE_PCD.
>> >
>> > The Linux kernel currently supports only 4 different cache modes. The PAT MSR
>> > is set up in a way that the setting of _PAGE_PAT in a pte doesn't matter: the
>> > top 4 entries in the PAT MSR are the same as the 4 lower entries.
>> >
>> > This results in the kernel not supporting e.g. write-through mode. Especially
>> > this cache mode would speed up drivers of video cards which now have to use
>> > uncached accesses.
>> >
>> > OTOH some old processors (Pentium) don't support PAT correctly and the Xen
>> > hypervisor has been using a different PAT MSR configuration for some time now
>> > and can't change that as this setting is part of the ABI.
>> >
>> > This patch set abstracts the cache mode from the pte and introduces tables to
>> > translate between cache mode and pte bits (the default cache mode "write back"
>> > is hard-wired to PAT entry 0). The tables are statically initialized with
>> > values being compatible to old processors and current usage. As soon as the
>> > PAT MSR is changed (or - in case of Xen - is read at boot time) the tables are
>> > changed accordingly. Requests of mappings with special cache modes are always
>> > possible now, in case they are not supported there will be a fallback to a
>> > compatible but slower mode.
>>
>> I feel like I'm missing something here.  Where's the support for the
>> high PAT bit on huge pages?  Once you start using the top four entries,
>> you'll need that.
>
> pgprot_4k_2_large() and pgprot_large_2_4k() provide the conversion of
> the PAT bit.

Whoops, I missed that.

>
>> Also, this probably needs errata handling.  IIRC there are a handful of
>> CPUs that support PAT but don't work correctly if the high bit is set.
>
> This patchset provides the infrastructure, but does not actually use the
> upper four entries.  I am working on additional patchset on top of this,
> which enables WT with the PAT bit except on the following Intel
> processors.  If I missed some processors affected, please let me know.
>
>   errata           cpuid
>   --------------------------------------
>   Pentium 2, A52   family 0x6, model 0x5
>   Pentium 3, E27   family 0x6, model 0x7
>   Pentium M, Y26   family 0x6, model 0x9
>   Pentium 4, N46   family 0xf, model 0x0
>

>From very vague memory, that sounds correct.

--Andy