Re: [PATCH 6/8] mm/highmem: make kmap cache coloring aware

From: Leonid Yegoshin <redacted>

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.

Cc: linux-mm@kvack.org
Cc: linux-arch@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Leonid Yegoshin <redacted>
[ Max: extract architecture-independent part of the original patch, clean
   up checkpatch and build warnings. ]
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes since the initial version:
- 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 | 19 ++++++++++++++++---
  1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..88fb62e 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c

@@ -44,6 +44,14 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
   */
  #ifdef CONFIG_HIGHMEM
  
+#ifndef ARCH_PKMAP_COLORING
+#define set_pkmap_color(pg, cl)		do { } while (0)
+#define get_last_pkmap_nr(p, cl)	(p)
+#define get_next_pkmap_nr(p, cl)	(((p) + 1) & LAST_PKMAP_MASK)
+#define no_more_pkmaps(p, cl)		(!(p))
+#define get_next_pkmap_counter(c, cl)	((c) - 1)
+#endif
+
  unsigned long totalhigh_pages __read_mostly;
  EXPORT_SYMBOL(totalhigh_pages);
  

@@ -161,19 +169,24 @@ static inline unsigned long map_new_virtual(struct page *page)
  {
  	unsigned long vaddr;
  	int count;
+	int color __maybe_unused;
+
+	set_pkmap_color(page, color);
+	last_pkmap_nr = get_last_pkmap_nr(last_pkmap_nr, color);
  
  start:
  	count = LAST_PKMAP;
  	/* 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(last_pkmap_nr, color);
+		if (no_more_pkmaps(last_pkmap_nr, color)) {
  			flush_all_zero_pkmaps();
  			count = LAST_PKMAP;
  		}
  		if (!pkmap_count[last_pkmap_nr])
  			break;	/* Found a usable entry */
-		if (--count)
+		count = get_next_pkmap_counter(count, color);
+		if (count)
  			continue;
  
  		/*