[PATCH v3 0/2] mm/highmem: make kmap cache coloring aware

[PATCH v3 0/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

Hi,

this series adds mapping color control to the generic kmap code, allowing
architectures with aliasing VIPT cache to use high memory. There's also
use example of this new interface by xtensa.

Max Filippov (2):
  mm/highmem: make kmap cache coloring aware
  xtensa: support aliasing cache in kmap

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++-
 arch/xtensa/mm/highmem.c          | 18 ++++++++
 mm/highmem.c                      | 89 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 134 insertions(+), 13 deletions(-)

-- 
1.8.1.4

[PATCH v3 0/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

Hi,

this series adds mapping color control to the generic kmap code, allowing
architectures with aliasing VIPT cache to use high memory. There's also
use example of this new interface by xtensa.

Max Filippov (2):
  mm/highmem: make kmap cache coloring aware
  xtensa: support aliasing cache in kmap

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++-
 arch/xtensa/mm/highmem.c          | 18 ++++++++
 mm/highmem.c                      | 89 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 134 insertions(+), 13 deletions(-)

-- 
1.8.1.4

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[PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

VIPT cache with way size larger than MMU page size may suffer from
aliasing problem: a single physical address accessed via different
virtual addresses may end up in multiple locations in the cache.
Virtual mappings of a physical address that always get cached in
different cache locations are said to have different colors.
L1 caching hardware usually doesn't handle this situation leaving it
up to software. Software must avoid this situation as it leads to
data corruption.

One way to handle this is to flush and invalidate data cache every time
page mapping changes color. The other way is to always map physical page
at a virtual address with the same color. Low memory pages already have
this property. Giving architecture a way to control color of high memory
page mapping allows reusing of existing low memory cache alias handling
code.

Provide hooks that allow architectures with aliasing cache to align
mapping address of high pages according to their color. Such architectures
may enforce similar coloring of low- and high-memory page mappings and
reuse existing cache management functions to support highmem.

This code is based on the implementation of similar feature for MIPS by
Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
- add comment stating that arch should place definitions into
  asm/highmem.h, include it directly to mm/highmem.c;
- replace macros with inline functions, change set_pkmap_color to
  get_pkmap_color which better fits inline function model;
- drop get_last_pkmap_nr;
- replace get_next_pkmap_counter with get_pkmap_entries_count, leave
  original counting code;
- introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
  on mapping color;
- move file-scope static variables last_pkmap_nr and pkmap_map_wait into
  get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
- document new functions;
- expand patch description and change authorship.

Changes v1->v2:
- define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
- rename is_no_more_pkmaps to no_more_pkmaps;
- change 'if (count > 0)' to 'if (count)' to better match the original
  code behavior;

 mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 78 insertions(+), 11 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..0d0cbbb 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -28,6 +28,9 @@
 #include <linux/highmem.h>
 #include <linux/kgdb.h>
 #include <asm/tlbflush.h>
+#ifdef CONFIG_HIGHMEM
+#include <asm/highmem.h>
+#endif
 
 
 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
@@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
  */
 #ifdef CONFIG_HIGHMEM
 
+/*
+ * Architecture with aliasing data cache may define the following family of
+ * helper functions in its asm/highmem.h to control cache color of virtual
+ * addresses where physical memory pages are mapped by kmap.
+ */
+#ifndef get_pkmap_color
+
+/*
+ * Determine color of virtual address where the page should be mapped.
+ */
+static inline unsigned int get_pkmap_color(struct page *page)
+{
+	return 0;
+}
+#define get_pkmap_color get_pkmap_color
+
+/*
+ * Get next index for mapping inside PKMAP region for page with given color.
+ */
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	static unsigned int last_pkmap_nr;
+
+	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
+	return last_pkmap_nr;
+}
+
+/*
+ * Determine if page index inside PKMAP region (pkmap_nr) of given color
+ * has wrapped around PKMAP region end. When this happens an attempt to
+ * flush all unused PKMAP slots is made.
+ */
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr == 0;
+}
+
+/*
+ * Get the number of PKMAP entries of the given color. If no free slot is
+ * found after checking that much entries, kmap will sleep waiting for
+ * someone to call kunmap and free PKMAP slot.
+ */
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP;
+}
+
+/*
+ * Get head of a wait queue for PKMAP entries of the given color.
+ * Wait queues for different mapping colors should be independent to avoid
+ * unnecessary wakeups caused by freeing of slots of other colors.
+ */
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
+
+	return &pkmap_map_wait;
+}
+#endif
+
 unsigned long totalhigh_pages __read_mostly;
 EXPORT_SYMBOL(totalhigh_pages);
 
@@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
 }
 
 static int pkmap_count[LAST_PKMAP];
-static unsigned int last_pkmap_nr;
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
 
 pte_t * pkmap_page_table;
 
-static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
-
 /*
  * Most architectures have no use for kmap_high_get(), so let's abstract
  * the disabling of IRQ out of the locking in that case to save on a
@@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;
 	int count;
+	unsigned int last_pkmap_nr;
+	unsigned int color = get_pkmap_color(page);
 
 start:
-	count = LAST_PKMAP;
+	count = get_pkmap_entries_count(color);
 	/* Find an empty entry */
 	for (;;) {
-		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
-		if (!last_pkmap_nr) {
+		last_pkmap_nr = get_next_pkmap_nr(color);
+		if (no_more_pkmaps(last_pkmap_nr, color)) {
 			flush_all_zero_pkmaps();
-			count = LAST_PKMAP;
+			count = get_pkmap_entries_count(color);
 		}
 		if (!pkmap_count[last_pkmap_nr])
 			break;	/* Found a usable entry */
@@ -181,12 +243,14 @@ start:
 		 */
 		{
 			DECLARE_WAITQUEUE(wait, current);
+			wait_queue_head_t *pkmap_map_wait =
+				get_pkmap_wait_queue_head(color);
 
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			add_wait_queue(&pkmap_map_wait, &wait);
+			add_wait_queue(pkmap_map_wait, &wait);
 			unlock_kmap();
 			schedule();
-			remove_wait_queue(&pkmap_map_wait, &wait);
+			remove_wait_queue(pkmap_map_wait, &wait);
 			lock_kmap();
 
 			/* Somebody else might have mapped it while we slept */
@@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
 	unsigned long nr;
 	unsigned long flags;
 	int need_wakeup;
+	unsigned int color = get_pkmap_color(page);
+	wait_queue_head_t *pkmap_map_wait;
 
 	lock_kmap_any(flags);
 	vaddr = (unsigned long)page_address(page);
@@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
 		 * no need for the wait-queue-head's lock.  Simply
 		 * test if the queue is empty.
 		 */
-		need_wakeup = waitqueue_active(&pkmap_map_wait);
+		pkmap_map_wait = get_pkmap_wait_queue_head(color);
+		need_wakeup = waitqueue_active(pkmap_map_wait);
 	}
 	unlock_kmap_any(flags);
 
 	/* do wake-up, if needed, race-free outside of the spin lock */
 	if (need_wakeup)
-		wake_up(&pkmap_map_wait);
+		wake_up(pkmap_map_wait);
 }
 
 EXPORT_SYMBOL(kunmap_high);
-- 
1.8.1.4

[PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

VIPT cache with way size larger than MMU page size may suffer from
aliasing problem: a single physical address accessed via different
virtual addresses may end up in multiple locations in the cache.
Virtual mappings of a physical address that always get cached in
different cache locations are said to have different colors.
L1 caching hardware usually doesn't handle this situation leaving it
up to software. Software must avoid this situation as it leads to
data corruption.

One way to handle this is to flush and invalidate data cache every time
page mapping changes color. The other way is to always map physical page
at a virtual address with the same color. Low memory pages already have
this property. Giving architecture a way to control color of high memory
page mapping allows reusing of existing low memory cache alias handling
code.

Provide hooks that allow architectures with aliasing cache to align
mapping address of high pages according to their color. Such architectures
may enforce similar coloring of low- and high-memory page mappings and
reuse existing cache management functions to support highmem.

This code is based on the implementation of similar feature for MIPS by
Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
- add comment stating that arch should place definitions into
  asm/highmem.h, include it directly to mm/highmem.c;
- replace macros with inline functions, change set_pkmap_color to
  get_pkmap_color which better fits inline function model;
- drop get_last_pkmap_nr;
- replace get_next_pkmap_counter with get_pkmap_entries_count, leave
  original counting code;
- introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
  on mapping color;
- move file-scope static variables last_pkmap_nr and pkmap_map_wait into
  get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
- document new functions;
- expand patch description and change authorship.

Changes v1->v2:
- define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
- rename is_no_more_pkmaps to no_more_pkmaps;
- change 'if (count > 0)' to 'if (count)' to better match the original
  code behavior;

 mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 78 insertions(+), 11 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..0d0cbbb 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -28,6 +28,9 @@
 #include <linux/highmem.h>
 #include <linux/kgdb.h>
 #include <asm/tlbflush.h>
+#ifdef CONFIG_HIGHMEM
+#include <asm/highmem.h>
+#endif
 
 
 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
@@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
  */
 #ifdef CONFIG_HIGHMEM
 
+/*
+ * Architecture with aliasing data cache may define the following family of
+ * helper functions in its asm/highmem.h to control cache color of virtual
+ * addresses where physical memory pages are mapped by kmap.
+ */
+#ifndef get_pkmap_color
+
+/*
+ * Determine color of virtual address where the page should be mapped.
+ */
+static inline unsigned int get_pkmap_color(struct page *page)
+{
+	return 0;
+}
+#define get_pkmap_color get_pkmap_color
+
+/*
+ * Get next index for mapping inside PKMAP region for page with given color.
+ */
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	static unsigned int last_pkmap_nr;
+
+	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
+	return last_pkmap_nr;
+}
+
+/*
+ * Determine if page index inside PKMAP region (pkmap_nr) of given color
+ * has wrapped around PKMAP region end. When this happens an attempt to
+ * flush all unused PKMAP slots is made.
+ */
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr == 0;
+}
+
+/*
+ * Get the number of PKMAP entries of the given color. If no free slot is
+ * found after checking that much entries, kmap will sleep waiting for
+ * someone to call kunmap and free PKMAP slot.
+ */
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP;
+}
+
+/*
+ * Get head of a wait queue for PKMAP entries of the given color.
+ * Wait queues for different mapping colors should be independent to avoid
+ * unnecessary wakeups caused by freeing of slots of other colors.
+ */
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
+
+	return &pkmap_map_wait;
+}
+#endif
+
 unsigned long totalhigh_pages __read_mostly;
 EXPORT_SYMBOL(totalhigh_pages);
 
@@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
 }
 
 static int pkmap_count[LAST_PKMAP];
-static unsigned int last_pkmap_nr;
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
 
 pte_t * pkmap_page_table;
 
-static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
-
 /*
  * Most architectures have no use for kmap_high_get(), so let's abstract
  * the disabling of IRQ out of the locking in that case to save on a
@@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;
 	int count;
+	unsigned int last_pkmap_nr;
+	unsigned int color = get_pkmap_color(page);
 
 start:
-	count = LAST_PKMAP;
+	count = get_pkmap_entries_count(color);
 	/* Find an empty entry */
 	for (;;) {
-		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
-		if (!last_pkmap_nr) {
+		last_pkmap_nr = get_next_pkmap_nr(color);
+		if (no_more_pkmaps(last_pkmap_nr, color)) {
 			flush_all_zero_pkmaps();
-			count = LAST_PKMAP;
+			count = get_pkmap_entries_count(color);
 		}
 		if (!pkmap_count[last_pkmap_nr])
 			break;	/* Found a usable entry */
@@ -181,12 +243,14 @@ start:
 		 */
 		{
 			DECLARE_WAITQUEUE(wait, current);
+			wait_queue_head_t *pkmap_map_wait =
+				get_pkmap_wait_queue_head(color);
 
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			add_wait_queue(&pkmap_map_wait, &wait);
+			add_wait_queue(pkmap_map_wait, &wait);
 			unlock_kmap();
 			schedule();
-			remove_wait_queue(&pkmap_map_wait, &wait);
+			remove_wait_queue(pkmap_map_wait, &wait);
 			lock_kmap();
 
 			/* Somebody else might have mapped it while we slept */
@@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
 	unsigned long nr;
 	unsigned long flags;
 	int need_wakeup;
+	unsigned int color = get_pkmap_color(page);
+	wait_queue_head_t *pkmap_map_wait;
 
 	lock_kmap_any(flags);
 	vaddr = (unsigned long)page_address(page);
@@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
 		 * no need for the wait-queue-head's lock.  Simply
 		 * test if the queue is empty.
 		 */
-		need_wakeup = waitqueue_active(&pkmap_map_wait);
+		pkmap_map_wait = get_pkmap_wait_queue_head(color);
+		need_wakeup = waitqueue_active(pkmap_map_wait);
 	}
 	unlock_kmap_any(flags);
 
 	/* do wake-up, if needed, race-free outside of the spin lock */
 	if (need_wakeup)
-		wake_up(&pkmap_map_wait);
+		wake_up(pkmap_map_wait);
 }
 
 EXPORT_SYMBOL(kunmap_high);
-- 
1.8.1.4

[PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

VIPT cache with way size larger than MMU page size may suffer from
aliasing problem: a single physical address accessed via different
virtual addresses may end up in multiple locations in the cache.
Virtual mappings of a physical address that always get cached in
different cache locations are said to have different colors.
L1 caching hardware usually doesn't handle this situation leaving it
up to software. Software must avoid this situation as it leads to
data corruption.

One way to handle this is to flush and invalidate data cache every time
page mapping changes color. The other way is to always map physical page
at a virtual address with the same color. Low memory pages already have
this property. Giving architecture a way to control color of high memory
page mapping allows reusing of existing low memory cache alias handling
code.

Provide hooks that allow architectures with aliasing cache to align
mapping address of high pages according to their color. Such architectures
may enforce similar coloring of low- and high-memory page mappings and
reuse existing cache management functions to support highmem.

This code is based on the implementation of similar feature for MIPS by
Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
- add comment stating that arch should place definitions into
  asm/highmem.h, include it directly to mm/highmem.c;
- replace macros with inline functions, change set_pkmap_color to
  get_pkmap_color which better fits inline function model;
- drop get_last_pkmap_nr;
- replace get_next_pkmap_counter with get_pkmap_entries_count, leave
  original counting code;
- introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
  on mapping color;
- move file-scope static variables last_pkmap_nr and pkmap_map_wait into
  get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
- document new functions;
- expand patch description and change authorship.

Changes v1->v2:
- define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
- rename is_no_more_pkmaps to no_more_pkmaps;
- change 'if (count > 0)' to 'if (count)' to better match the original
  code behavior;

 mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 78 insertions(+), 11 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..0d0cbbb 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -28,6 +28,9 @@
 #include <linux/highmem.h>
 #include <linux/kgdb.h>
 #include <asm/tlbflush.h>
+#ifdef CONFIG_HIGHMEM
+#include <asm/highmem.h>
+#endif
 
 
 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
@@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
  */
 #ifdef CONFIG_HIGHMEM
 
+/*
+ * Architecture with aliasing data cache may define the following family of
+ * helper functions in its asm/highmem.h to control cache color of virtual
+ * addresses where physical memory pages are mapped by kmap.
+ */
+#ifndef get_pkmap_color
+
+/*
+ * Determine color of virtual address where the page should be mapped.
+ */
+static inline unsigned int get_pkmap_color(struct page *page)
+{
+	return 0;
+}
+#define get_pkmap_color get_pkmap_color
+
+/*
+ * Get next index for mapping inside PKMAP region for page with given color.
+ */
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	static unsigned int last_pkmap_nr;
+
+	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
+	return last_pkmap_nr;
+}
+
+/*
+ * Determine if page index inside PKMAP region (pkmap_nr) of given color
+ * has wrapped around PKMAP region end. When this happens an attempt to
+ * flush all unused PKMAP slots is made.
+ */
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr == 0;
+}
+
+/*
+ * Get the number of PKMAP entries of the given color. If no free slot is
+ * found after checking that much entries, kmap will sleep waiting for
+ * someone to call kunmap and free PKMAP slot.
+ */
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP;
+}
+
+/*
+ * Get head of a wait queue for PKMAP entries of the given color.
+ * Wait queues for different mapping colors should be independent to avoid
+ * unnecessary wakeups caused by freeing of slots of other colors.
+ */
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
+
+	return &pkmap_map_wait;
+}
+#endif
+
 unsigned long totalhigh_pages __read_mostly;
 EXPORT_SYMBOL(totalhigh_pages);
 
@@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
 }
 
 static int pkmap_count[LAST_PKMAP];
-static unsigned int last_pkmap_nr;
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
 
 pte_t * pkmap_page_table;
 
-static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
-
 /*
  * Most architectures have no use for kmap_high_get(), so let's abstract
  * the disabling of IRQ out of the locking in that case to save on a
@@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;
 	int count;
+	unsigned int last_pkmap_nr;
+	unsigned int color = get_pkmap_color(page);
 
 start:
-	count = LAST_PKMAP;
+	count = get_pkmap_entries_count(color);
 	/* Find an empty entry */
 	for (;;) {
-		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
-		if (!last_pkmap_nr) {
+		last_pkmap_nr = get_next_pkmap_nr(color);
+		if (no_more_pkmaps(last_pkmap_nr, color)) {
 			flush_all_zero_pkmaps();
-			count = LAST_PKMAP;
+			count = get_pkmap_entries_count(color);
 		}
 		if (!pkmap_count[last_pkmap_nr])
 			break;	/* Found a usable entry */
@@ -181,12 +243,14 @@ start:
 		 */
 		{
 			DECLARE_WAITQUEUE(wait, current);
+			wait_queue_head_t *pkmap_map_wait =
+				get_pkmap_wait_queue_head(color);
 
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			add_wait_queue(&pkmap_map_wait, &wait);
+			add_wait_queue(pkmap_map_wait, &wait);
 			unlock_kmap();
 			schedule();
-			remove_wait_queue(&pkmap_map_wait, &wait);
+			remove_wait_queue(pkmap_map_wait, &wait);
 			lock_kmap();
 
 			/* Somebody else might have mapped it while we slept */
@@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
 	unsigned long nr;
 	unsigned long flags;
 	int need_wakeup;
+	unsigned int color = get_pkmap_color(page);
+	wait_queue_head_t *pkmap_map_wait;
 
 	lock_kmap_any(flags);
 	vaddr = (unsigned long)page_address(page);
@@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
 		 * no need for the wait-queue-head's lock.  Simply
 		 * test if the queue is empty.
 		 */
-		need_wakeup = waitqueue_active(&pkmap_map_wait);
+		pkmap_map_wait = get_pkmap_wait_queue_head(color);
+		need_wakeup = waitqueue_active(pkmap_map_wait);
 	}
 	unlock_kmap_any(flags);
 
 	/* do wake-up, if needed, race-free outside of the spin lock */
 	if (need_wakeup)
-		wake_up(&pkmap_map_wait);
+		wake_up(pkmap_map_wait);
 }
 
 EXPORT_SYMBOL(kunmap_high);
-- 
1.8.1.4

[PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

VIPT cache with way size larger than MMU page size may suffer from
aliasing problem: a single physical address accessed via different
virtual addresses may end up in multiple locations in the cache.
Virtual mappings of a physical address that always get cached in
different cache locations are said to have different colors.
L1 caching hardware usually doesn't handle this situation leaving it
up to software. Software must avoid this situation as it leads to
data corruption.

One way to handle this is to flush and invalidate data cache every time
page mapping changes color. The other way is to always map physical page
at a virtual address with the same color. Low memory pages already have
this property. Giving architecture a way to control color of high memory
page mapping allows reusing of existing low memory cache alias handling
code.

Provide hooks that allow architectures with aliasing cache to align
mapping address of high pages according to their color. Such architectures
may enforce similar coloring of low- and high-memory page mappings and
reuse existing cache management functions to support highmem.

This code is based on the implementation of similar feature for MIPS by
Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
- add comment stating that arch should place definitions into
  asm/highmem.h, include it directly to mm/highmem.c;
- replace macros with inline functions, change set_pkmap_color to
  get_pkmap_color which better fits inline function model;
- drop get_last_pkmap_nr;
- replace get_next_pkmap_counter with get_pkmap_entries_count, leave
  original counting code;
- introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
  on mapping color;
- move file-scope static variables last_pkmap_nr and pkmap_map_wait into
  get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
- document new functions;
- expand patch description and change authorship.

Changes v1->v2:
- define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
- rename is_no_more_pkmaps to no_more_pkmaps;
- change 'if (count > 0)' to 'if (count)' to better match the original
  code behavior;

 mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 78 insertions(+), 11 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..0d0cbbb 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -28,6 +28,9 @@
 #include <linux/highmem.h>
 #include <linux/kgdb.h>
 #include <asm/tlbflush.h>
+#ifdef CONFIG_HIGHMEM
+#include <asm/highmem.h>
+#endif
 
 
 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
@@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
  */
 #ifdef CONFIG_HIGHMEM
 
+/*
+ * Architecture with aliasing data cache may define the following family of
+ * helper functions in its asm/highmem.h to control cache color of virtual
+ * addresses where physical memory pages are mapped by kmap.
+ */
+#ifndef get_pkmap_color
+
+/*
+ * Determine color of virtual address where the page should be mapped.
+ */
+static inline unsigned int get_pkmap_color(struct page *page)
+{
+	return 0;
+}
+#define get_pkmap_color get_pkmap_color
+
+/*
+ * Get next index for mapping inside PKMAP region for page with given color.
+ */
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	static unsigned int last_pkmap_nr;
+
+	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
+	return last_pkmap_nr;
+}
+
+/*
+ * Determine if page index inside PKMAP region (pkmap_nr) of given color
+ * has wrapped around PKMAP region end. When this happens an attempt to
+ * flush all unused PKMAP slots is made.
+ */
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr == 0;
+}
+
+/*
+ * Get the number of PKMAP entries of the given color. If no free slot is
+ * found after checking that much entries, kmap will sleep waiting for
+ * someone to call kunmap and free PKMAP slot.
+ */
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP;
+}
+
+/*
+ * Get head of a wait queue for PKMAP entries of the given color.
+ * Wait queues for different mapping colors should be independent to avoid
+ * unnecessary wakeups caused by freeing of slots of other colors.
+ */
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
+
+	return &pkmap_map_wait;
+}
+#endif
+
 unsigned long totalhigh_pages __read_mostly;
 EXPORT_SYMBOL(totalhigh_pages);
 
@@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
 }
 
 static int pkmap_count[LAST_PKMAP];
-static unsigned int last_pkmap_nr;
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
 
 pte_t * pkmap_page_table;
 
-static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
-
 /*
  * Most architectures have no use for kmap_high_get(), so let's abstract
  * the disabling of IRQ out of the locking in that case to save on a
@@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;
 	int count;
+	unsigned int last_pkmap_nr;
+	unsigned int color = get_pkmap_color(page);
 
 start:
-	count = LAST_PKMAP;
+	count = get_pkmap_entries_count(color);
 	/* Find an empty entry */
 	for (;;) {
-		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
-		if (!last_pkmap_nr) {
+		last_pkmap_nr = get_next_pkmap_nr(color);
+		if (no_more_pkmaps(last_pkmap_nr, color)) {
 			flush_all_zero_pkmaps();
-			count = LAST_PKMAP;
+			count = get_pkmap_entries_count(color);
 		}
 		if (!pkmap_count[last_pkmap_nr])
 			break;	/* Found a usable entry */
@@ -181,12 +243,14 @@ start:
 		 */
 		{
 			DECLARE_WAITQUEUE(wait, current);
+			wait_queue_head_t *pkmap_map_wait =
+				get_pkmap_wait_queue_head(color);
 
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			add_wait_queue(&pkmap_map_wait, &wait);
+			add_wait_queue(pkmap_map_wait, &wait);
 			unlock_kmap();
 			schedule();
-			remove_wait_queue(&pkmap_map_wait, &wait);
+			remove_wait_queue(pkmap_map_wait, &wait);
 			lock_kmap();
 
 			/* Somebody else might have mapped it while we slept */
@@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
 	unsigned long nr;
 	unsigned long flags;
 	int need_wakeup;
+	unsigned int color = get_pkmap_color(page);
+	wait_queue_head_t *pkmap_map_wait;
 
 	lock_kmap_any(flags);
 	vaddr = (unsigned long)page_address(page);
@@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
 		 * no need for the wait-queue-head's lock.  Simply
 		 * test if the queue is empty.
 		 */
-		need_wakeup = waitqueue_active(&pkmap_map_wait);
+		pkmap_map_wait = get_pkmap_wait_queue_head(color);
+		need_wakeup = waitqueue_active(pkmap_map_wait);
 	}
 	unlock_kmap_any(flags);
 
 	/* do wake-up, if needed, race-free outside of the spin lock */
 	if (need_wakeup)
-		wake_up(&pkmap_map_wait);
+		wake_up(pkmap_map_wait);
 }
 
 EXPORT_SYMBOL(kunmap_high);
-- 
1.8.1.4

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[PATCH v3 2/2] xtensa: support aliasing cache in kmap

[Max Filippov]

Define ARCH_PKMAP_COLORING and provide corresponding macro definitions
on cores with aliasing data cache.

Instead of single last_pkmap_nr maintain an array last_pkmap_nr_arr of
pkmap counters for each page color. Make sure that kmap maps physical
page at virtual address with color matching its physical address.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- switch to new function names/prototypes;
- implement get_pkmap_wait_queue_head, add kmap_waitqueues_init.

Changes v1->v2:
- new file.

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++++++++++++++++++++++--
 arch/xtensa/mm/highmem.c          | 18 ++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/include/asm/highmem.h b/arch/xtensa/include/asm/highmem.h
index 2653ef5..2c7901e 100644
--- a/arch/xtensa/include/asm/highmem.h
+++ b/arch/xtensa/include/asm/highmem.h
@@ -12,19 +12,55 @@
 #ifndef _XTENSA_HIGHMEM_H
 #define _XTENSA_HIGHMEM_H
 
+#include <linux/wait.h>
 #include <asm/cacheflush.h>
 #include <asm/fixmap.h>
 #include <asm/kmap_types.h>
 #include <asm/pgtable.h>
 
-#define PKMAP_BASE		(FIXADDR_START - PMD_SIZE)
-#define LAST_PKMAP		PTRS_PER_PTE
+#define PKMAP_BASE		((FIXADDR_START - \
+				  (LAST_PKMAP + 1) * PAGE_SIZE) & PMD_MASK)
+#define LAST_PKMAP		(PTRS_PER_PTE * DCACHE_N_COLORS)
 #define LAST_PKMAP_MASK		(LAST_PKMAP - 1)
 #define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
 #define kmap_prot		PAGE_KERNEL
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+#define get_pkmap_color get_pkmap_color
+static inline int get_pkmap_color(struct page *page)
+{
+	return DCACHE_ALIAS(page_to_phys(page));
+}
+
+extern unsigned int last_pkmap_nr_arr[];
+
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	last_pkmap_nr_arr[color] =
+		(last_pkmap_nr_arr[color] + DCACHE_N_COLORS) & LAST_PKMAP_MASK;
+	return last_pkmap_nr_arr[color] + color;
+}
+
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr < DCACHE_N_COLORS;
+}
+
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP / DCACHE_N_COLORS;
+}
+
+extern wait_queue_head_t pkmap_map_wait_arr[];
+
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	return pkmap_map_wait_arr + color;
+}
+#endif
+
 extern pte_t *pkmap_page_table;
 
 void *kmap_high(struct page *page);
diff --git a/arch/xtensa/mm/highmem.c b/arch/xtensa/mm/highmem.c
index 466abae..8cfb71e 100644
--- a/arch/xtensa/mm/highmem.c
+++ b/arch/xtensa/mm/highmem.c
@@ -14,6 +14,23 @@
 
 static pte_t *kmap_pte;
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+unsigned int last_pkmap_nr_arr[DCACHE_N_COLORS];
+wait_queue_head_t pkmap_map_wait_arr[DCACHE_N_COLORS];
+
+static void __init kmap_waitqueues_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(pkmap_map_wait_arr); ++i)
+		init_waitqueue_head(pkmap_map_wait_arr + i);
+}
+#else
+static inline void kmap_waitqueues_init(void)
+{
+}
+#endif
+
 static inline enum fixed_addresses kmap_idx(int type, unsigned long color)
 {
 	return (type + KM_TYPE_NR * smp_processor_id()) * DCACHE_N_COLORS +
@@ -72,4 +89,5 @@ void __init kmap_init(void)
 	/* cache the first kmap pte */
 	kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
 	kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
+	kmap_waitqueues_init();
 }
-- 
1.8.1.4

[PATCH v3 2/2] xtensa: support aliasing cache in kmap

[Max Filippov]

Define ARCH_PKMAP_COLORING and provide corresponding macro definitions
on cores with aliasing data cache.

Instead of single last_pkmap_nr maintain an array last_pkmap_nr_arr of
pkmap counters for each page color. Make sure that kmap maps physical
page at virtual address with color matching its physical address.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- switch to new function names/prototypes;
- implement get_pkmap_wait_queue_head, add kmap_waitqueues_init.

Changes v1->v2:
- new file.

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++++++++++++++++++++++--
 arch/xtensa/mm/highmem.c          | 18 ++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/include/asm/highmem.h b/arch/xtensa/include/asm/highmem.h
index 2653ef5..2c7901e 100644
--- a/arch/xtensa/include/asm/highmem.h
+++ b/arch/xtensa/include/asm/highmem.h
@@ -12,19 +12,55 @@
 #ifndef _XTENSA_HIGHMEM_H
 #define _XTENSA_HIGHMEM_H
 
+#include <linux/wait.h>
 #include <asm/cacheflush.h>
 #include <asm/fixmap.h>
 #include <asm/kmap_types.h>
 #include <asm/pgtable.h>
 
-#define PKMAP_BASE		(FIXADDR_START - PMD_SIZE)
-#define LAST_PKMAP		PTRS_PER_PTE
+#define PKMAP_BASE		((FIXADDR_START - \
+				  (LAST_PKMAP + 1) * PAGE_SIZE) & PMD_MASK)
+#define LAST_PKMAP		(PTRS_PER_PTE * DCACHE_N_COLORS)
 #define LAST_PKMAP_MASK		(LAST_PKMAP - 1)
 #define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
 #define kmap_prot		PAGE_KERNEL
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+#define get_pkmap_color get_pkmap_color
+static inline int get_pkmap_color(struct page *page)
+{
+	return DCACHE_ALIAS(page_to_phys(page));
+}
+
+extern unsigned int last_pkmap_nr_arr[];
+
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	last_pkmap_nr_arr[color] =
+		(last_pkmap_nr_arr[color] + DCACHE_N_COLORS) & LAST_PKMAP_MASK;
+	return last_pkmap_nr_arr[color] + color;
+}
+
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr < DCACHE_N_COLORS;
+}
+
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP / DCACHE_N_COLORS;
+}
+
+extern wait_queue_head_t pkmap_map_wait_arr[];
+
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	return pkmap_map_wait_arr + color;
+}
+#endif
+
 extern pte_t *pkmap_page_table;
 
 void *kmap_high(struct page *page);
diff --git a/arch/xtensa/mm/highmem.c b/arch/xtensa/mm/highmem.c
index 466abae..8cfb71e 100644
--- a/arch/xtensa/mm/highmem.c
+++ b/arch/xtensa/mm/highmem.c
@@ -14,6 +14,23 @@
 
 static pte_t *kmap_pte;
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+unsigned int last_pkmap_nr_arr[DCACHE_N_COLORS];
+wait_queue_head_t pkmap_map_wait_arr[DCACHE_N_COLORS];
+
+static void __init kmap_waitqueues_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(pkmap_map_wait_arr); ++i)
+		init_waitqueue_head(pkmap_map_wait_arr + i);
+}
+#else
+static inline void kmap_waitqueues_init(void)
+{
+}
+#endif
+
 static inline enum fixed_addresses kmap_idx(int type, unsigned long color)
 {
 	return (type + KM_TYPE_NR * smp_processor_id()) * DCACHE_N_COLORS +
@@ -72,4 +89,5 @@ void __init kmap_init(void)
 	/* cache the first kmap pte */
 	kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
 	kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
+	kmap_waitqueues_init();
 }
-- 
1.8.1.4

[PATCH v3 2/2] xtensa: support aliasing cache in kmap

[Max Filippov]

Define ARCH_PKMAP_COLORING and provide corresponding macro definitions
on cores with aliasing data cache.

Instead of single last_pkmap_nr maintain an array last_pkmap_nr_arr of
pkmap counters for each page color. Make sure that kmap maps physical
page at virtual address with color matching its physical address.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- switch to new function names/prototypes;
- implement get_pkmap_wait_queue_head, add kmap_waitqueues_init.

Changes v1->v2:
- new file.

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++++++++++++++++++++++--
 arch/xtensa/mm/highmem.c          | 18 ++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/include/asm/highmem.h b/arch/xtensa/include/asm/highmem.h
index 2653ef5..2c7901e 100644
--- a/arch/xtensa/include/asm/highmem.h
+++ b/arch/xtensa/include/asm/highmem.h
@@ -12,19 +12,55 @@
 #ifndef _XTENSA_HIGHMEM_H
 #define _XTENSA_HIGHMEM_H
 
+#include <linux/wait.h>
 #include <asm/cacheflush.h>
 #include <asm/fixmap.h>
 #include <asm/kmap_types.h>
 #include <asm/pgtable.h>
 
-#define PKMAP_BASE		(FIXADDR_START - PMD_SIZE)
-#define LAST_PKMAP		PTRS_PER_PTE
+#define PKMAP_BASE		((FIXADDR_START - \
+				  (LAST_PKMAP + 1) * PAGE_SIZE) & PMD_MASK)
+#define LAST_PKMAP		(PTRS_PER_PTE * DCACHE_N_COLORS)
 #define LAST_PKMAP_MASK		(LAST_PKMAP - 1)
 #define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
 #define kmap_prot		PAGE_KERNEL
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+#define get_pkmap_color get_pkmap_color
+static inline int get_pkmap_color(struct page *page)
+{
+	return DCACHE_ALIAS(page_to_phys(page));
+}
+
+extern unsigned int last_pkmap_nr_arr[];
+
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	last_pkmap_nr_arr[color] =
+		(last_pkmap_nr_arr[color] + DCACHE_N_COLORS) & LAST_PKMAP_MASK;
+	return last_pkmap_nr_arr[color] + color;
+}
+
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr < DCACHE_N_COLORS;
+}
+
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP / DCACHE_N_COLORS;
+}
+
+extern wait_queue_head_t pkmap_map_wait_arr[];
+
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	return pkmap_map_wait_arr + color;
+}
+#endif
+
 extern pte_t *pkmap_page_table;
 
 void *kmap_high(struct page *page);
diff --git a/arch/xtensa/mm/highmem.c b/arch/xtensa/mm/highmem.c
index 466abae..8cfb71e 100644
--- a/arch/xtensa/mm/highmem.c
+++ b/arch/xtensa/mm/highmem.c
@@ -14,6 +14,23 @@
 
 static pte_t *kmap_pte;
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+unsigned int last_pkmap_nr_arr[DCACHE_N_COLORS];
+wait_queue_head_t pkmap_map_wait_arr[DCACHE_N_COLORS];
+
+static void __init kmap_waitqueues_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(pkmap_map_wait_arr); ++i)
+		init_waitqueue_head(pkmap_map_wait_arr + i);
+}
+#else
+static inline void kmap_waitqueues_init(void)
+{
+}
+#endif
+
 static inline enum fixed_addresses kmap_idx(int type, unsigned long color)
 {
 	return (type + KM_TYPE_NR * smp_processor_id()) * DCACHE_N_COLORS +
@@ -72,4 +89,5 @@ void __init kmap_init(void)
 	/* cache the first kmap pte */
 	kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
 	kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
+	kmap_waitqueues_init();
 }
-- 
1.8.1.4

[PATCH v3 2/2] xtensa: support aliasing cache in kmap

[Max Filippov]

Define ARCH_PKMAP_COLORING and provide corresponding macro definitions
on cores with aliasing data cache.

Instead of single last_pkmap_nr maintain an array last_pkmap_nr_arr of
pkmap counters for each page color. Make sure that kmap maps physical
page at virtual address with color matching its physical address.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v2->v3:
- switch to new function names/prototypes;
- implement get_pkmap_wait_queue_head, add kmap_waitqueues_init.

Changes v1->v2:
- new file.

 arch/xtensa/include/asm/highmem.h | 40 +++++++++++++++++++++++++++++++++++++--
 arch/xtensa/mm/highmem.c          | 18 ++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/include/asm/highmem.h b/arch/xtensa/include/asm/highmem.h
index 2653ef5..2c7901e 100644
--- a/arch/xtensa/include/asm/highmem.h
+++ b/arch/xtensa/include/asm/highmem.h
@@ -12,19 +12,55 @@
 #ifndef _XTENSA_HIGHMEM_H
 #define _XTENSA_HIGHMEM_H
 
+#include <linux/wait.h>
 #include <asm/cacheflush.h>
 #include <asm/fixmap.h>
 #include <asm/kmap_types.h>
 #include <asm/pgtable.h>
 
-#define PKMAP_BASE		(FIXADDR_START - PMD_SIZE)
-#define LAST_PKMAP		PTRS_PER_PTE
+#define PKMAP_BASE		((FIXADDR_START - \
+				  (LAST_PKMAP + 1) * PAGE_SIZE) & PMD_MASK)
+#define LAST_PKMAP		(PTRS_PER_PTE * DCACHE_N_COLORS)
 #define LAST_PKMAP_MASK		(LAST_PKMAP - 1)
 #define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
 #define kmap_prot		PAGE_KERNEL
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+#define get_pkmap_color get_pkmap_color
+static inline int get_pkmap_color(struct page *page)
+{
+	return DCACHE_ALIAS(page_to_phys(page));
+}
+
+extern unsigned int last_pkmap_nr_arr[];
+
+static inline unsigned int get_next_pkmap_nr(unsigned int color)
+{
+	last_pkmap_nr_arr[color] =
+		(last_pkmap_nr_arr[color] + DCACHE_N_COLORS) & LAST_PKMAP_MASK;
+	return last_pkmap_nr_arr[color] + color;
+}
+
+static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
+{
+	return pkmap_nr < DCACHE_N_COLORS;
+}
+
+static inline int get_pkmap_entries_count(unsigned int color)
+{
+	return LAST_PKMAP / DCACHE_N_COLORS;
+}
+
+extern wait_queue_head_t pkmap_map_wait_arr[];
+
+static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
+{
+	return pkmap_map_wait_arr + color;
+}
+#endif
+
 extern pte_t *pkmap_page_table;
 
 void *kmap_high(struct page *page);
diff --git a/arch/xtensa/mm/highmem.c b/arch/xtensa/mm/highmem.c
index 466abae..8cfb71e 100644
--- a/arch/xtensa/mm/highmem.c
+++ b/arch/xtensa/mm/highmem.c
@@ -14,6 +14,23 @@
 
 static pte_t *kmap_pte;
 
+#if DCACHE_WAY_SIZE > PAGE_SIZE
+unsigned int last_pkmap_nr_arr[DCACHE_N_COLORS];
+wait_queue_head_t pkmap_map_wait_arr[DCACHE_N_COLORS];
+
+static void __init kmap_waitqueues_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(pkmap_map_wait_arr); ++i)
+		init_waitqueue_head(pkmap_map_wait_arr + i);
+}
+#else
+static inline void kmap_waitqueues_init(void)
+{
+}
+#endif
+
 static inline enum fixed_addresses kmap_idx(int type, unsigned long color)
 {
 	return (type + KM_TYPE_NR * smp_processor_id()) * DCACHE_N_COLORS +
@@ -72,4 +89,5 @@ void __init kmap_init(void)
 	/* cache the first kmap pte */
 	kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
 	kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
+	kmap_waitqueues_init();
 }
-- 
1.8.1.4

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Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

On Fri, Jul 25, 2014 at 11:43 PM, Max Filippov <jcmvbkbc@gmail.com> wrote:
> VIPT cache with way size larger than MMU page size may suffer from
> aliasing problem: a single physical address accessed via different
> virtual addresses may end up in multiple locations in the cache.
> Virtual mappings of a physical address that always get cached in
> different cache locations are said to have different colors.
> L1 caching hardware usually doesn't handle this situation leaving it
> up to software. Software must avoid this situation as it leads to
> data corruption.
>
> One way to handle this is to flush and invalidate data cache every time
> page mapping changes color. The other way is to always map physical page
> at a virtual address with the same color. Low memory pages already have
> this property. Giving architecture a way to control color of high memory
> page mapping allows reusing of existing low memory cache alias handling
> code.
>
> Provide hooks that allow architectures with aliasing cache to align
> mapping address of high pages according to their color. Such architectures
> may enforce similar coloring of low- and high-memory page mappings and
> reuse existing cache management functions to support highmem.
>
> This code is based on the implementation of similar feature for MIPS by
> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---

Ping? Is there anything else that can help making this patch better
and getting it merged?

> Changes v2->v3:
> - drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
> - add comment stating that arch should place definitions into
>   asm/highmem.h, include it directly to mm/highmem.c;
> - replace macros with inline functions, change set_pkmap_color to
>   get_pkmap_color which better fits inline function model;
> - drop get_last_pkmap_nr;
> - replace get_next_pkmap_counter with get_pkmap_entries_count, leave
>   original counting code;
> - introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
>   on mapping color;
> - move file-scope static variables last_pkmap_nr and pkmap_map_wait into
>   get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
> - document new functions;
> - expand patch description and change authorship.
>
> Changes v1->v2:
> - define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
> - rename is_no_more_pkmaps to no_more_pkmaps;
> - change 'if (count > 0)' to 'if (count)' to better match the original
>   code behavior;
>
>  mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 78 insertions(+), 11 deletions(-)
>
> diff --git a/mm/highmem.c b/mm/highmem.c
> index b32b70c..0d0cbbb 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -28,6 +28,9 @@
>  #include <linux/highmem.h>
>  #include <linux/kgdb.h>
>  #include <asm/tlbflush.h>
> +#ifdef CONFIG_HIGHMEM
> +#include <asm/highmem.h>
> +#endif
>
>
>  #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
> @@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
>   */
>  #ifdef CONFIG_HIGHMEM
>
> +/*
> + * Architecture with aliasing data cache may define the following family of
> + * helper functions in its asm/highmem.h to control cache color of virtual
> + * addresses where physical memory pages are mapped by kmap.
> + */
> +#ifndef get_pkmap_color
> +
> +/*
> + * Determine color of virtual address where the page should be mapped.
> + */
> +static inline unsigned int get_pkmap_color(struct page *page)
> +{
> +       return 0;
> +}
> +#define get_pkmap_color get_pkmap_color
> +
> +/*
> + * Get next index for mapping inside PKMAP region for page with given color.
> + */
> +static inline unsigned int get_next_pkmap_nr(unsigned int color)
> +{
> +       static unsigned int last_pkmap_nr;
> +
> +       last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> +       return last_pkmap_nr;
> +}
> +
> +/*
> + * Determine if page index inside PKMAP region (pkmap_nr) of given color
> + * has wrapped around PKMAP region end. When this happens an attempt to
> + * flush all unused PKMAP slots is made.
> + */
> +static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
> +{
> +       return pkmap_nr == 0;
> +}
> +
> +/*
> + * Get the number of PKMAP entries of the given color. If no free slot is
> + * found after checking that much entries, kmap will sleep waiting for
> + * someone to call kunmap and free PKMAP slot.
> + */
> +static inline int get_pkmap_entries_count(unsigned int color)
> +{
> +       return LAST_PKMAP;
> +}
> +
> +/*
> + * Get head of a wait queue for PKMAP entries of the given color.
> + * Wait queues for different mapping colors should be independent to avoid
> + * unnecessary wakeups caused by freeing of slots of other colors.
> + */
> +static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
> +{
> +       static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
> +
> +       return &pkmap_map_wait;
> +}
> +#endif
> +
>  unsigned long totalhigh_pages __read_mostly;
>  EXPORT_SYMBOL(totalhigh_pages);
>
> @@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
>  }
>
>  static int pkmap_count[LAST_PKMAP];
> -static unsigned int last_pkmap_nr;
>  static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
>
>  pte_t * pkmap_page_table;
>
> -static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
> -
>  /*
>   * Most architectures have no use for kmap_high_get(), so let's abstract
>   * the disabling of IRQ out of the locking in that case to save on a
> @@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
>  {
>         unsigned long vaddr;
>         int count;
> +       unsigned int last_pkmap_nr;
> +       unsigned int color = get_pkmap_color(page);
>
>  start:
> -       count = LAST_PKMAP;
> +       count = get_pkmap_entries_count(color);
>         /* Find an empty entry */
>         for (;;) {
> -               last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> -               if (!last_pkmap_nr) {
> +               last_pkmap_nr = get_next_pkmap_nr(color);
> +               if (no_more_pkmaps(last_pkmap_nr, color)) {
>                         flush_all_zero_pkmaps();
> -                       count = LAST_PKMAP;
> +                       count = get_pkmap_entries_count(color);
>                 }
>                 if (!pkmap_count[last_pkmap_nr])
>                         break;  /* Found a usable entry */
> @@ -181,12 +243,14 @@ start:
>                  */
>                 {
>                         DECLARE_WAITQUEUE(wait, current);
> +                       wait_queue_head_t *pkmap_map_wait =
> +                               get_pkmap_wait_queue_head(color);
>
>                         __set_current_state(TASK_UNINTERRUPTIBLE);
> -                       add_wait_queue(&pkmap_map_wait, &wait);
> +                       add_wait_queue(pkmap_map_wait, &wait);
>                         unlock_kmap();
>                         schedule();
> -                       remove_wait_queue(&pkmap_map_wait, &wait);
> +                       remove_wait_queue(pkmap_map_wait, &wait);
>                         lock_kmap();
>
>                         /* Somebody else might have mapped it while we slept */
> @@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
>         unsigned long nr;
>         unsigned long flags;
>         int need_wakeup;
> +       unsigned int color = get_pkmap_color(page);
> +       wait_queue_head_t *pkmap_map_wait;
>
>         lock_kmap_any(flags);
>         vaddr = (unsigned long)page_address(page);
> @@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
>                  * no need for the wait-queue-head's lock.  Simply
>                  * test if the queue is empty.
>                  */
> -               need_wakeup = waitqueue_active(&pkmap_map_wait);
> +               pkmap_map_wait = get_pkmap_wait_queue_head(color);
> +               need_wakeup = waitqueue_active(pkmap_map_wait);
>         }
>         unlock_kmap_any(flags);
>
>         /* do wake-up, if needed, race-free outside of the spin lock */
>         if (need_wakeup)
> -               wake_up(&pkmap_map_wait);
> +               wake_up(pkmap_map_wait);
>  }
>
>  EXPORT_SYMBOL(kunmap_high);
> --
> 1.8.1.4
>



-- 
Thanks.
-- Max

Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

On Fri, Jul 25, 2014 at 11:43 PM, Max Filippov <jcmvbkbc@gmail.com> wrote:
> VIPT cache with way size larger than MMU page size may suffer from
> aliasing problem: a single physical address accessed via different
> virtual addresses may end up in multiple locations in the cache.
> Virtual mappings of a physical address that always get cached in
> different cache locations are said to have different colors.
> L1 caching hardware usually doesn't handle this situation leaving it
> up to software. Software must avoid this situation as it leads to
> data corruption.
>
> One way to handle this is to flush and invalidate data cache every time
> page mapping changes color. The other way is to always map physical page
> at a virtual address with the same color. Low memory pages already have
> this property. Giving architecture a way to control color of high memory
> page mapping allows reusing of existing low memory cache alias handling
> code.
>
> Provide hooks that allow architectures with aliasing cache to align
> mapping address of high pages according to their color. Such architectures
> may enforce similar coloring of low- and high-memory page mappings and
> reuse existing cache management functions to support highmem.
>
> This code is based on the implementation of similar feature for MIPS by
> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---

Ping? Is there anything else that can help making this patch better
and getting it merged?

> Changes v2->v3:
> - drop ARCH_PKMAP_COLORING, check gif et_pkmap_color is defined instead;
> - add comment stating that arch should place definitions into
>   asm/highmem.h, include it directly to mm/highmem.c;
> - replace macros with inline functions, change set_pkmap_color to
>   get_pkmap_color which better fits inline function model;
> - drop get_last_pkmap_nr;
> - replace get_next_pkmap_counter with get_pkmap_entries_count, leave
>   original counting code;
> - introduce get_pkmap_wait_queue_head and make sleeping/waking dependent
>   on mapping color;
> - move file-scope static variables last_pkmap_nr and pkmap_map_wait into
>   get_next_pkmap_nr and get_pkmap_wait_queue_head respectively;
> - document new functions;
> - expand patch description and change authorship.
>
> Changes v1->v2:
> - define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
> - rename is_no_more_pkmaps to no_more_pkmaps;
> - change 'if (count > 0)' to 'if (count)' to better match the original
>   code behavior;
>
>  mm/highmem.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 78 insertions(+), 11 deletions(-)
>
> diff --git a/mm/highmem.c b/mm/highmem.c
> index b32b70c..0d0cbbb 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -28,6 +28,9 @@
>  #include <linux/highmem.h>
>  #include <linux/kgdb.h>
>  #include <asm/tlbflush.h>
> +#ifdef CONFIG_HIGHMEM
> +#include <asm/highmem.h>
> +#endif
>
>
>  #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
> @@ -44,6 +47,66 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
>   */
>  #ifdef CONFIG_HIGHMEM
>
> +/*
> + * Architecture with aliasing data cache may define the following family of
> + * helper functions in its asm/highmem.h to control cache color of virtual
> + * addresses where physical memory pages are mapped by kmap.
> + */
> +#ifndef get_pkmap_color
> +
> +/*
> + * Determine color of virtual address where the page should be mapped.
> + */
> +static inline unsigned int get_pkmap_color(struct page *page)
> +{
> +       return 0;
> +}
> +#define get_pkmap_color get_pkmap_color
> +
> +/*
> + * Get next index for mapping inside PKMAP region for page with given color.
> + */
> +static inline unsigned int get_next_pkmap_nr(unsigned int color)
> +{
> +       static unsigned int last_pkmap_nr;
> +
> +       last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> +       return last_pkmap_nr;
> +}
> +
> +/*
> + * Determine if page index inside PKMAP region (pkmap_nr) of given color
> + * has wrapped around PKMAP region end. When this happens an attempt to
> + * flush all unused PKMAP slots is made.
> + */
> +static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
> +{
> +       return pkmap_nr == 0;
> +}
> +
> +/*
> + * Get the number of PKMAP entries of the given color. If no free slot is
> + * found after checking that much entries, kmap will sleep waiting for
> + * someone to call kunmap and free PKMAP slot.
> + */
> +static inline int get_pkmap_entries_count(unsigned int color)
> +{
> +       return LAST_PKMAP;
> +}
> +
> +/*
> + * Get head of a wait queue for PKMAP entries of the given color.
> + * Wait queues for different mapping colors should be independent to avoid
> + * unnecessary wakeups caused by freeing of slots of other colors.
> + */
> +static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
> +{
> +       static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
> +
> +       return &pkmap_map_wait;
> +}
> +#endif
> +
>  unsigned long totalhigh_pages __read_mostly;
>  EXPORT_SYMBOL(totalhigh_pages);
>
> @@ -68,13 +131,10 @@ unsigned int nr_free_highpages (void)
>  }
>
>  static int pkmap_count[LAST_PKMAP];
> -static unsigned int last_pkmap_nr;
>  static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
>
>  pte_t * pkmap_page_table;
>
> -static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
> -
>  /*
>   * Most architectures have no use for kmap_high_get(), so let's abstract
>   * the disabling of IRQ out of the locking in that case to save on a
> @@ -161,15 +221,17 @@ static inline unsigned long map_new_virtual(struct page *page)
>  {
>         unsigned long vaddr;
>         int count;
> +       unsigned int last_pkmap_nr;
> +       unsigned int color = get_pkmap_color(page);
>
>  start:
> -       count = LAST_PKMAP;
> +       count = get_pkmap_entries_count(color);
>         /* Find an empty entry */
>         for (;;) {
> -               last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> -               if (!last_pkmap_nr) {
> +               last_pkmap_nr = get_next_pkmap_nr(color);
> +               if (no_more_pkmaps(last_pkmap_nr, color)) {
>                         flush_all_zero_pkmaps();
> -                       count = LAST_PKMAP;
> +                       count = get_pkmap_entries_count(color);
>                 }
>                 if (!pkmap_count[last_pkmap_nr])
>                         break;  /* Found a usable entry */
> @@ -181,12 +243,14 @@ start:
>                  */
>                 {
>                         DECLARE_WAITQUEUE(wait, current);
> +                       wait_queue_head_t *pkmap_map_wait =
> +                               get_pkmap_wait_queue_head(color);
>
>                         __set_current_state(TASK_UNINTERRUPTIBLE);
> -                       add_wait_queue(&pkmap_map_wait, &wait);
> +                       add_wait_queue(pkmap_map_wait, &wait);
>                         unlock_kmap();
>                         schedule();
> -                       remove_wait_queue(&pkmap_map_wait, &wait);
> +                       remove_wait_queue(pkmap_map_wait, &wait);
>                         lock_kmap();
>
>                         /* Somebody else might have mapped it while we slept */
> @@ -274,6 +338,8 @@ void kunmap_high(struct page *page)
>         unsigned long nr;
>         unsigned long flags;
>         int need_wakeup;
> +       unsigned int color = get_pkmap_color(page);
> +       wait_queue_head_t *pkmap_map_wait;
>
>         lock_kmap_any(flags);
>         vaddr = (unsigned long)page_address(page);
> @@ -299,13 +365,14 @@ void kunmap_high(struct page *page)
>                  * no need for the wait-queue-head's lock.  Simply
>                  * test if the queue is empty.
>                  */
> -               need_wakeup = waitqueue_active(&pkmap_map_wait);
> +               pkmap_map_wait = get_pkmap_wait_queue_head(color);
> +               need_wakeup = waitqueue_active(pkmap_map_wait);
>         }
>         unlock_kmap_any(flags);
>
>         /* do wake-up, if needed, race-free outside of the spin lock */
>         if (need_wakeup)
> -               wake_up(&pkmap_map_wait);
> +               wake_up(pkmap_map_wait);
>  }
>
>  EXPORT_SYMBOL(kunmap_high);
> --
> 1.8.1.4
>



-- 
Thanks.
-- Max

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Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Andrew Morton]

On Fri, 25 Jul 2014 23:43:46 +0400 Max Filippov <jcmvbkbc@gmail.com> wrote:

> VIPT cache with way size larger than MMU page size may suffer from
> aliasing problem: a single physical address accessed via different
> virtual addresses may end up in multiple locations in the cache.
> Virtual mappings of a physical address that always get cached in
> different cache locations are said to have different colors.
> L1 caching hardware usually doesn't handle this situation leaving it
> up to software. Software must avoid this situation as it leads to
> data corruption.
> 
> One way to handle this is to flush and invalidate data cache every time
> page mapping changes color. The other way is to always map physical page
> at a virtual address with the same color. Low memory pages already have
> this property. Giving architecture a way to control color of high memory
> page mapping allows reusing of existing low memory cache alias handling
> code.
> 
> Provide hooks that allow architectures with aliasing cache to align
> mapping address of high pages according to their color. Such architectures
> may enforce similar coloring of low- and high-memory page mappings and
> reuse existing cache management functions to support highmem.
> 
> This code is based on the implementation of similar feature for MIPS by
> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
> 

It's worth mentioning that xtensa needs this.

What is (still) missing from these changelogs is a clear description of
the end-user visible effects.  Does it fix some bug?  If so what?  Is
it a performace optimisation?  If so how much?  This info is the
top-line reason for the patchset and should be presented as such.

> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -28,6 +28,9 @@
>  #include <linux/highmem.h>
>  #include <linux/kgdb.h>
>  #include <asm/tlbflush.h>
> +#ifdef CONFIG_HIGHMEM
> +#include <asm/highmem.h>
> +#endif

Should be unneeded - the linux/highmem.h inclusion already did this.

Apart from that it all looks OK to me.  I'm assuming this is 3.17-rc1
material, but I am unsure because of the missing end-user-impact info. 
If it's needed in earlier kernels then we can tag it for -stable
backporting but again, the -stable team (ie: Greg) will want so see the
justification for that backport.

Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Andrew Morton]

On Fri, 25 Jul 2014 23:43:46 +0400 Max Filippov <jcmvbkbc@gmail.com> wrote:

> VIPT cache with way size larger than MMU page size may suffer from
> aliasing problem: a single physical address accessed via different
> virtual addresses may end up in multiple locations in the cache.
> Virtual mappings of a physical address that always get cached in
> different cache locations are said to have different colors.
> L1 caching hardware usually doesn't handle this situation leaving it
> up to software. Software must avoid this situation as it leads to
> data corruption.
> 
> One way to handle this is to flush and invalidate data cache every time
> page mapping changes color. The other way is to always map physical page
> at a virtual address with the same color. Low memory pages already have
> this property. Giving architecture a way to control color of high memory
> page mapping allows reusing of existing low memory cache alias handling
> code.
> 
> Provide hooks that allow architectures with aliasing cache to align
> mapping address of high pages according to their color. Such architectures
> may enforce similar coloring of low- and high-memory page mappings and
> reuse existing cache management functions to support highmem.
> 
> This code is based on the implementation of similar feature for MIPS by
> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
> 

It's worth mentioning that xtensa needs this.

What is (still) missing from these changelogs is a clear description of
the end-user visible effects.  Does it fix some bug?  If so what?  Is
it a performace optimisation?  If so how much?  This info is the
top-line reason for the patchset and should be presented as such.

> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -28,6 +28,9 @@
>  #include <linux/highmem.h>
>  #include <linux/kgdb.h>
>  #include <asm/tlbflush.h>
> +#ifdef CONFIG_HIGHMEM
> +#include <asm/highmem.h>
> +#endif

Should be unneeded - the linux/highmem.h inclusion already did this.

Apart from that it all looks OK to me.  I'm assuming this is 3.17-rc1
material, but I am unsure because of the missing end-user-impact info. 
If it's needed in earlier kernels then we can tag it for -stable
backporting but again, the -stable team (ie: Greg) will want so see the
justification for that backport.

--
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Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

On Sat, Aug 2, 2014 at 12:10 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Fri, 25 Jul 2014 23:43:46 +0400 Max Filippov <jcmvbkbc@gmail.com> wrote:
>
>> VIPT cache with way size larger than MMU page size may suffer from
>> aliasing problem: a single physical address accessed via different
>> virtual addresses may end up in multiple locations in the cache.
>> Virtual mappings of a physical address that always get cached in
>> different cache locations are said to have different colors.
>> L1 caching hardware usually doesn't handle this situation leaving it
>> up to software. Software must avoid this situation as it leads to
>> data corruption.
>>
>> One way to handle this is to flush and invalidate data cache every time
>> page mapping changes color. The other way is to always map physical page
>> at a virtual address with the same color. Low memory pages already have
>> this property. Giving architecture a way to control color of high memory
>> page mapping allows reusing of existing low memory cache alias handling
>> code.
>>
>> Provide hooks that allow architectures with aliasing cache to align
>> mapping address of high pages according to their color. Such architectures
>> may enforce similar coloring of low- and high-memory page mappings and
>> reuse existing cache management functions to support highmem.
>>
>> This code is based on the implementation of similar feature for MIPS by
>> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
>>
>
> It's worth mentioning that xtensa needs this.
>
> What is (still) missing from these changelogs is a clear description of
> the end-user visible effects.  Does it fix some bug?  If so what?  Is
> it a performace optimisation?  If so how much?  This info is the
> top-line reason for the patchset and should be presented as such.

Ok, let me try again.

>> --- a/mm/highmem.c
>> +++ b/mm/highmem.c
>> @@ -28,6 +28,9 @@
>>  #include <linux/highmem.h>
>>  #include <linux/kgdb.h>
>>  #include <asm/tlbflush.h>
>> +#ifdef CONFIG_HIGHMEM
>> +#include <asm/highmem.h>
>> +#endif
>
> Should be unneeded - the linux/highmem.h inclusion already did this.

Ok, I'll drop it.

> Apart from that it all looks OK to me.  I'm assuming this is 3.17-rc1
> material, but I am unsure because of the missing end-user-impact info.
> If it's needed in earlier kernels then we can tag it for -stable
> backporting but again, the -stable team (ie: Greg) will want so see the
> justification for that backport.

It's not a fix, for xtensa it's a part of a new feature, so no need
for backporting.

-- 
Thanks.
-- Max

Re: [PATCH v3 1/2] mm/highmem: make kmap cache coloring aware

[Max Filippov]

On Sat, Aug 2, 2014 at 12:10 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Fri, 25 Jul 2014 23:43:46 +0400 Max Filippov <jcmvbkbc@gmail.com> wrote:
>
>> VIPT cache with way size larger than MMU page size may suffer from
>> aliasing problem: a single physical address accessed via different
>> virtual addresses may end up in multiple locations in the cache.
>> Virtual mappings of a physical address that always get cached in
>> different cache locations are said to have different colors.
>> L1 caching hardware usually doesn't handle this situation leaving it
>> up to software. Software must avoid this situation as it leads to
>> data corruption.
>>
>> One way to handle this is to flush and invalidate data cache every time
>> page mapping changes color. The other way is to always map physical page
>> at a virtual address with the same color. Low memory pages already have
>> this property. Giving architecture a way to control color of high memory
>> page mapping allows reusing of existing low memory cache alias handling
>> code.
>>
>> Provide hooks that allow architectures with aliasing cache to align
>> mapping address of high pages according to their color. Such architectures
>> may enforce similar coloring of low- and high-memory page mappings and
>> reuse existing cache management functions to support highmem.
>>
>> This code is based on the implementation of similar feature for MIPS by
>> Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>.
>>
>
> It's worth mentioning that xtensa needs this.
>
> What is (still) missing from these changelogs is a clear description of
> the end-user visible effects.  Does it fix some bug?  If so what?  Is
> it a performace optimisation?  If so how much?  This info is the
> top-line reason for the patchset and should be presented as such.

Ok, let me try again.

>> --- a/mm/highmem.c
>> +++ b/mm/highmem.c
>> @@ -28,6 +28,9 @@
>>  #include <linux/highmem.h>
>>  #include <linux/kgdb.h>
>>  #include <asm/tlbflush.h>
>> +#ifdef CONFIG_HIGHMEM
>> +#include <asm/highmem.h>
>> +#endif
>
> Should be unneeded - the linux/highmem.h inclusion already did this.

Ok, I'll drop it.

> Apart from that it all looks OK to me.  I'm assuming this is 3.17-rc1
> material, but I am unsure because of the missing end-user-impact info.
> If it's needed in earlier kernels then we can tag it for -stable
> backporting but again, the -stable team (ie: Greg) will want so see the
> justification for that backport.

It's not a fix, for xtensa it's a part of a new feature, so no need
for backporting.

-- 
Thanks.
-- Max

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