sh: Handle fixmap TLB eviction more coherently.

There was a race in the kmap_coherent() implementation. While we
guarded against preemption, there was nothing preventing eviction of
the pre-faulted fixmap entry from the UTLB. Under certain workloads
this would result in the fixmap entries used for cache colouring being
evicted from the UTLB in the midst of a copy_page().

In addition to pre-faulting, we also make sure to preserve the PTEs
in the kernel page table and introduce a cached PTE for kmap_coherent()
usage. This follows a similar change on MIPS ("[MIPS] Fix aliasing bug
in copy_to_user_page / copy_from_user_page").

Reported-by: Hideo Saito <saito@densan.co.jp>
Reported-by: CHIKAMA Masaki <masaki.chikama@gmail.com>
Tested-by: Yoshihiro Shimoda <shimoda.yoshihiro@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

3 files changed, 32 insertions, 3 deletions

diff --git a/arch/sh/include/asm/pgtable.h b/arch/sh/include/asm/pgtable.h
index 52220d70a096..b517ae08b9c0 100644
--- a/arch/sh/include/asm/pgtable.h
+++ b/arch/sh/include/asm/pgtable.h
@@ -148,6 +148,12 @@ extern void paging_init(void);
 extern void page_table_range_init(unsigned long start, unsigned long end,
                                   pgd_t *pgd);
 
+#if !defined(CONFIG_CACHE_OFF) && defined(CONFIG_CPU_SH4) && defined(CONFIG_MMU)
+extern void kmap_coherent_init(void);
+#else
+#define kmap_coherent_init()    do { } while (0)
+#endif
+
 #include <asm-generic/pgtable.h>
 
 #endif /* __ASM_SH_PGTABLE_H */
diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
index 4abf00031dae..6cbef8caeb56 100644
--- a/arch/sh/mm/init.c
+++ b/arch/sh/mm/init.c
@@ -137,6 +137,7 @@ void __init page_table_range_init(unsigned long start, unsigned long end,
 void __init paging_init(void)
 {
         unsigned long max_zone_pfns[MAX_NR_ZONES];
+        unsigned long vaddr;
         int nid;
 
         /* We don't need to map the kernel through the TLB, as
@@ -148,10 +149,15 @@ void __init paging_init(void)
          * check for a null value. */
         set_TTB(swapper_pg_dir);
 
-        /* Populate the relevant portions of swapper_pg_dir so that
+        /*
+         * Populate the relevant portions of swapper_pg_dir so that
          * we can use the fixmap entries without calling kmalloc.
-         * pte's will be filled in by __set_fixmap(). */
-        page_table_range_init(FIXADDR_START, FIXADDR_TOP, swapper_pg_dir);
+         * pte's will be filled in by __set_fixmap().
+         */
+        vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
+        page_table_range_init(vaddr, 0, swapper_pg_dir);
+
+        kmap_coherent_init();
 
         memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
 
diff --git a/arch/sh/mm/pg-sh4.c b/arch/sh/mm/pg-sh4.c
index 38870e0fc182..2fe14da1f839 100644
--- a/arch/sh/mm/pg-sh4.c
+++ b/arch/sh/mm/pg-sh4.c
@@ -7,6 +7,7 @@
  * Released under the terms of the GNU GPL v2.0.
  */
 #include <linux/mm.h>
+#include <linux/init.h>
 #include <linux/mutex.h>
 #include <linux/fs.h>
 #include <linux/highmem.h>
@@ -16,6 +17,20 @@
 
 #define CACHE_ALIAS (current_cpu_data.dcache.alias_mask)
 
+#define kmap_get_fixmap_pte(vaddr)                                     \
+        pte_offset_kernel(pmd_offset(pud_offset(pgd_offset_k(vaddr), (vaddr)), (vaddr)), (vaddr))
+
+static pte_t *kmap_coherent_pte;
+
+void __init kmap_coherent_init(void)
+{
+        unsigned long vaddr;
+
+        /* cache the first coherent kmap pte */
+        vaddr = __fix_to_virt(FIX_CMAP_BEGIN);
+        kmap_coherent_pte = kmap_get_fixmap_pte(vaddr);
+}
+
 static inline void *kmap_coherent(struct page *page, unsigned long addr)
 {
         enum fixed_addresses idx;
@@ -34,6 +49,8 @@ static inline void *kmap_coherent(struct page *page, unsigned long addr)
 
         update_mmu_cache(NULL, vaddr, pte);
 
+        set_pte(kmap_coherent_pte - (FIX_CMAP_END - idx), pte);
+
         return (void *)vaddr;
 }