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>

1 files changed, 17 insertions, 0 deletions

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;
 }