[4.4-rt2 PATCH] ARM: highmem: take into account FIX_KMAP_BEGIN in switch_kmaps()

[Grygorii Strashko <grygorii.strashko@ti.com>]

Now the random crashes are observed on ARM TI am437x-idk-evm used with
-RT Kernel v4.4-rt2 and with Highmem enabled.

The reason of issue is that, newly introduced switch_kmaps() does not
take into account FIX_KMAP_BEGIN, which was re-added by
commit a5f4c561b3b1 ("ARM: 8415/1: early fixmap support for earlycon")
(K4.3) for ARM and since that the value of FIX_KMAP_BEGIN
is not 0 any more.

Hence update switch_kmaps() so it will take into FIX_KMAP_BEGIN while
calculating fixmap idx. This patch also introduces fixmap_idx() to
make code simpler and remove duplicated code.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 arch/arm/mm/highmem.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index deabc36..542692d 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -34,6 +34,11 @@ static inline pte_t get_fixmap_pte(unsigned long vaddr)
 	return *ptep;
 }
 
+static unsigned int fixmap_idx(int type)
+{
+	return FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
+}
+
 void *kmap(struct page *page)
 {
 	might_sleep();
@@ -80,7 +85,7 @@ void *kmap_atomic(struct page *page)
 
 	type = kmap_atomic_idx_push();
 
-	idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
+	idx = fixmap_idx(type);
 	vaddr = __fix_to_virt(idx);
 #ifdef CONFIG_DEBUG_HIGHMEM
 	/*
@@ -110,7 +115,7 @@ void __kunmap_atomic(void *kvaddr)
 
 	if (kvaddr >= (void *)FIXADDR_START) {
 		type = kmap_atomic_idx();
-		idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
+		idx = fixmap_idx(type);
 
 		if (cache_is_vivt())
 			__cpuc_flush_dcache_area((void *)vaddr, PAGE_SIZE);
@@ -146,7 +151,7 @@ void *kmap_atomic_pfn(unsigned long pfn)
 		return page_address(page);
 
 	type = kmap_atomic_idx_push();
-	idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
+	idx = fixmap_idx(type);
 	vaddr = __fix_to_virt(idx);
 #ifdef CONFIG_DEBUG_HIGHMEM
 	BUG_ON(!pte_none(get_fixmap_pte(vaddr)));
@@ -167,7 +172,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
 	 * Clear @prev's kmap_atomic mappings
 	 */
 	for (i = 0; i < prev_p->kmap_idx; i++) {
-		int idx = i + KM_TYPE_NR * smp_processor_id();
+		int idx = fixmap_idx(i);
 
 		set_fixmap_pte(idx, __pte(0));
 	}
@@ -175,7 +180,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
 	 * Restore @next_p's kmap_atomic mappings
 	 */
 	for (i = 0; i < next_p->kmap_idx; i++) {
-		int idx = i + KM_TYPE_NR * smp_processor_id();
+		int idx = fixmap_idx(i);
 
 		if (!pte_none(next_p->kmap_pte[i]))
 			set_fixmap_pte(idx, next_p->kmap_pte[i]);
-- 
2.7.0