arm: mm: introduce special ptes for LPAE

We need a mechanism to tag ptes as being special, this indicates that no
attempt should be made to access the underlying struct page * associated
with the pte.  This is used by the fast_gup when operating on ptes as it
has no means to access VMAs (that also contain this information)
locklessly.

The L_PTE_SPECIAL bit is already allocated for LPAE, this patch modifies
pte_special and pte_mkspecial to make use of it, and defines
__HAVE_ARCH_PTE_SPECIAL.

This patch also excludes special ptes from the icache/dcache sync logic.

Signed-off-by: Steve Capper <steve.capper@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dann Frazier <dann.frazier@canonical.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 11 insertions, 4 deletions

diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
index 219ac88a9542..f0279411847d 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -182,6 +182,8 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 #define pmd_addr_end(addr,end) (end)
 
 #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
+#define pte_special(pte)        (0)
+static inline pte_t pte_mkspecial(pte_t pte) { return pte; }
 
 /*
  * We don't have huge page support for short descriptors, for the moment
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index 06e0bc0f8b00..16122d4d7081 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -213,6 +213,13 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 #define pmd_isclear(pmd, val)   (!(pmd_val(pmd) & (val)))
 
 #define pmd_young(pmd)          (pmd_isset((pmd), PMD_SECT_AF))
+#define pte_special(pte)        (pte_isset((pte), L_PTE_SPECIAL))
+static inline pte_t pte_mkspecial(pte_t pte)
+{
+        pte_val(pte) |= L_PTE_SPECIAL;
+        return pte;
+}
+#define __HAVE_ARCH_PTE_SPECIAL
 
 #define __HAVE_ARCH_PMD_WRITE
 #define pmd_write(pmd)          (pmd_isclear((pmd), L_PMD_SECT_RDONLY))
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 01baef07cd0c..90aa4583b308 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -226,7 +226,6 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd)
 #define pte_dirty(pte)          (pte_isset((pte), L_PTE_DIRTY))
 #define pte_young(pte)          (pte_isset((pte), L_PTE_YOUNG))
 #define pte_exec(pte)           (pte_isclear((pte), L_PTE_XN))
-#define pte_special(pte)        (0)
 
 #define pte_valid_user(pte)     \
         (pte_valid(pte) && pte_isset((pte), L_PTE_USER) && pte_young(pte))
@@ -245,7 +244,8 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
         unsigned long ext = 0;
 
         if (addr < TASK_SIZE && pte_valid_user(pteval)) {
-                __sync_icache_dcache(pteval);
+                if (!pte_special(pteval))
+                        __sync_icache_dcache(pteval);
                 ext |= PTE_EXT_NG;
         }
 
@@ -264,8 +264,6 @@ PTE_BIT_FUNC(mkyoung,   |= L_PTE_YOUNG);
 PTE_BIT_FUNC(mkexec,   &= ~L_PTE_XN);
 PTE_BIT_FUNC(mknexec,   |= L_PTE_XN);
 
-static inline pte_t pte_mkspecial(pte_t pte) { return pte; }
-
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
         const pteval_t mask = L_PTE_XN | L_PTE_RDONLY | L_PTE_USER |