xtensa/mm/highmem: Make generic kmap_atomic() work correctly

The conversion to the generic kmap_atomic() implementation missed the fact
that xtensa's fixmap works bottom up while all other implementations work
top down. There is no real reason why xtensa needs to work that way.

Cure it by:

  - Using the generic fix_to_virt()/virt_to_fix() functions which work top
    down
  - Adjusting the mapping defines
  - Using the generic index calculation for the non cache aliasing case
  - Making the cache colour offset reverse so the effective index is correct

While at it, remove the outdated and misleading comment above the fixmap
enum which originates from the initial copy&pasta of this code from i386.

[ Max: Fixed the off by one in the index calculation ]

Fixes: 629ed3f7dad2 ("xtensa/mm/highmem: Switch to generic kmap atomic")
Reported-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Max Filippov <jcmvbkbc@gmail.com>
Link: https://lore.kernel.org/r/20201116193253.23875-1-jcmvbkbc@gmail.com

3 files changed, 15 insertions, 10 deletions

diff --git a/arch/xtensa/mm/highmem.c b/arch/xtensa/mm/highmem.c
index 0735ca5e8f86..35c4f7d4a333 100644
--- a/arch/xtensa/mm/highmem.c
+++ b/arch/xtensa/mm/highmem.c
@@ -23,16 +23,16 @@ static void __init kmap_waitqueues_init(void)
 	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_MAX_IDX * smp_processor_id()) * DCACHE_N_COLORS +
-		color;
+	int idx = (type + KM_MAX_IDX * smp_processor_id()) * DCACHE_N_COLORS;
+
+	/*
+	 * The fixmap operates top down, so the color offset needs to be
+	 * reverse as well.
+	 */
+	return idx + DCACHE_N_COLORS - 1 - color;
 }
 
 enum fixed_addresses kmap_local_map_idx(int type, unsigned long pfn)
@@ -45,6 +45,10 @@ enum fixed_addresses kmap_local_unmap_idx(int type, unsigned long addr)
 	return kmap_idx(type, DCACHE_ALIAS(addr));
 }
 
+#else
+static inline void kmap_waitqueues_init(void) { }
+#endif
+
 void __init kmap_init(void)
 {
 	/* Check if this memory layout is broken because PKMAP overlaps
diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index c6fc83efee0c..0f85666bcbeb 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -147,8 +147,8 @@ void __init mem_init(void)
 #ifdef CONFIG_HIGHMEM
 		PKMAP_BASE, PKMAP_BASE + LAST_PKMAP * PAGE_SIZE,
 		(LAST_PKMAP*PAGE_SIZE) >> 10,
-		FIXADDR_START, FIXADDR_TOP,
-		(FIXADDR_TOP - FIXADDR_START) >> 10,
+		FIXADDR_START, FIXADDR_END,
+		(FIXADDR_END - FIXADDR_START) >> 10,
 #endif
 		PAGE_OFFSET, PAGE_OFFSET +
 		(max_low_pfn - min_low_pfn) * PAGE_SIZE,
diff --git a/arch/xtensa/mm/mmu.c b/arch/xtensa/mm/mmu.c
index fd2193df8a14..7e4d97dc8bd8 100644
--- a/arch/xtensa/mm/mmu.c
+++ b/arch/xtensa/mm/mmu.c
@@ -52,7 +52,8 @@ static void * __init init_pmd(unsigned long vaddr, unsigned long n_pages)
 
 static void __init fixedrange_init(void)
 {
-	init_pmd(__fix_to_virt(0), __end_of_fixed_addresses);
+	BUILD_BUG_ON(FIXADDR_START < TLBTEMP_BASE_1 + TLBTEMP_SIZE);
+	init_pmd(FIXADDR_START, __end_of_fixed_addresses);
 }
 #endif