[ARM] mm 3: separate out supersection mappings, avoid for <4GB

Catalin Marinas at ARM Ltd says:
> The CPU architects in ARM intended supersections only as a way to map
> addresses >= 4GB. Supersections are not mandated by the architecture
> and there is no easy way to detect their hardware support at run-time
> (other than checking for a specific core). From the analysis done in
> ARM, there wasn't a clear performance gain by using supersections
> rather than sections (no significant improvement in the TLB misses).

Therefore, we should avoid using supersections unless there's a real
need (iow, we're mapping addresses >= 4GB).

This means that we can simplify create_mapping() a bit since we will
only use supersection mappings for addresses >= 4GB, which means that
the physical, virtual and length must be multiples of the supersection
mapping size.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 62 insertions, 70 deletions

diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
index 0ac615c0f798..800855b2dc83 100644
--- a/arch/arm/mm/ioremap.c
+++ b/arch/arm/mm/ioremap.c
@@ -302,7 +302,7 @@ __ioremap_pfn(unsigned long pfn, unsigned long offset, size_t size,
 #ifndef CONFIG_SMP
         if (DOMAIN_IO == 0 &&
             (((cpu_architecture() >= CPU_ARCH_ARMv6) && (get_cr() & CR_XP)) ||
-               cpu_is_xsc3()) &&
+               cpu_is_xsc3()) && pfn >= 0x100000 &&
                !((__pfn_to_phys(pfn) | size | addr) & ~SUPERSECTION_MASK)) {
                 area->flags |= VM_ARM_SECTION_MAPPING;
                 err = remap_area_supersections(addr, pfn, size, flags);
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e359f3685433..32139800d939 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -398,21 +398,6 @@ alloc_init_section(unsigned long virt, unsigned long phys, int prot)
 }
 
 /*
- * Create a SUPER SECTION PGD between VIRT and PHYS with protection PROT
- */
-static inline void
-alloc_init_supersection(unsigned long virt, unsigned long phys, int prot)
-{
-        int i;
-
-        for (i = 0; i < 16; i += 1) {
-                alloc_init_section(virt, phys, prot | PMD_SECT_SUPER);
-
-                virt += (PGDIR_SIZE / 2);
-        }
-}
-
-/*
  * Add a PAGE mapping between VIRT and PHYS in domain
  * DOMAIN with protection PROT.  Note that due to the
  * way we map the PTEs, we must allocate two PTE_SIZE'd
@@ -436,6 +421,64 @@ alloc_init_page(unsigned long virt, unsigned long phys, const struct mem_type *t
         set_pte_ext(ptep, pfn_pte(phys >> PAGE_SHIFT, __pgprot(type->prot_pte)), 0);
 }
 
+static void __init create_36bit_mapping(struct map_desc *md,
+                                        const struct mem_type *type)
+{
+        unsigned long phys, addr, length, end;
+        pgd_t *pgd;
+
+        addr = md->virtual;
+        phys = (unsigned long)__pfn_to_phys(md->pfn);
+        length = PAGE_ALIGN(md->length);
+
+        if (!(cpu_architecture() >= CPU_ARCH_ARMv6 || cpu_is_xsc3())) {
+                printk(KERN_ERR "MM: CPU does not support supersection "
+                       "mapping for 0x%08llx at 0x%08lx\n",
+                       __pfn_to_phys((u64)md->pfn), addr);
+                return;
+        }
+
+        /* N.B. ARMv6 supersections are only defined to work with domain 0.
+         *      Since domain assignments can in fact be arbitrary, the
+         *      'domain == 0' check below is required to insure that ARMv6
+         *      supersections are only allocated for domain 0 regardless
+         *      of the actual domain assignments in use.
+         */
+        if (type->domain) {
+                printk(KERN_ERR "MM: invalid domain in supersection "
+                       "mapping for 0x%08llx at 0x%08lx\n",
+                       __pfn_to_phys((u64)md->pfn), addr);
+                return;
+        }
+
+        if ((addr | length | __pfn_to_phys(md->pfn)) & ~SUPERSECTION_MASK) {
+                printk(KERN_ERR "MM: cannot create mapping for "
+                       "0x%08llx at 0x%08lx invalid alignment\n",
+                       __pfn_to_phys((u64)md->pfn), addr);
+                return;
+        }
+
+        /*
+         * Shift bits [35:32] of address into bits [23:20] of PMD
+         * (See ARMv6 spec).
+         */
+        phys |= (((md->pfn >> (32 - PAGE_SHIFT)) & 0xF) << 20);
+
+        pgd = pgd_offset_k(addr);
+        end = addr + length;
+        do {
+                pmd_t *pmd = pmd_offset(pgd, addr);
+                int i;
+
+                for (i = 0; i < 16; i++)
+                        *pmd++ = __pmd(phys | type->prot_sect | PMD_SECT_SUPER);
+
+                addr += SUPERSECTION_SIZE;
+                phys += SUPERSECTION_SIZE;
+                pgd += SUPERSECTION_SIZE >> PGDIR_SHIFT;
+        } while (addr != end);
+}
+
 /*
  * Create the page directory entries and any necessary
  * page tables for the mapping specified by `md'.  We
@@ -468,26 +511,9 @@ void __init create_mapping(struct map_desc *md)
         /*
          * Catch 36-bit addresses
          */
-        if(md->pfn >= 0x100000) {
-                if (type->domain) {
-                        printk(KERN_ERR "MM: invalid domain in supersection "
-                                "mapping for 0x%08llx at 0x%08lx\n",
-                                __pfn_to_phys((u64)md->pfn), md->virtual);
-                        return;
-                }
-                if((md->virtual | md->length | __pfn_to_phys(md->pfn))
-                        & ~SUPERSECTION_MASK) {
-                        printk(KERN_ERR "MM: cannot create mapping for "
-                                "0x%08llx at 0x%08lx invalid alignment\n",
-                                __pfn_to_phys((u64)md->pfn), md->virtual);
-                        return;
-                }
-
-                /*
-                 * Shift bits [35:32] of address into bits [23:20] of PMD
-                 * (See ARMv6 spec).
-                 */
-                off |= (((md->pfn >> (32 - PAGE_SHIFT)) & 0xF) << 20);
+        if (md->pfn >= 0x100000) {
+                create_36bit_mapping(md, type);
+                return;
         }
 
         virt   = md->virtual;
@@ -509,40 +535,6 @@ void __init create_mapping(struct map_desc *md)
                 length -= PAGE_SIZE;
         }
 
-        /* N.B. ARMv6 supersections are only defined to work with domain 0.
-         *      Since domain assignments can in fact be arbitrary, the
-         *      'domain == 0' check below is required to insure that ARMv6
-         *      supersections are only allocated for domain 0 regardless
-         *      of the actual domain assignments in use.
-         */
-        if ((cpu_architecture() >= CPU_ARCH_ARMv6 || cpu_is_xsc3())
-                && type->domain == 0) {
-                /*
-                 * Align to supersection boundary if !high pages.
-                 * High pages have already been checked for proper
-                 * alignment above and they will fail the SUPSERSECTION_MASK
-                 * check because of the way the address is encoded into
-                 * offset.
-                 */
-                if (md->pfn <= 0x100000) {
-                        while ((virt & ~SUPERSECTION_MASK ||
-                                (virt + off) & ~SUPERSECTION_MASK) &&
-                                length >= (PGDIR_SIZE / 2)) {
-                                alloc_init_section(virt, virt + off, type->prot_sect);
-
-                                virt   += (PGDIR_SIZE / 2);
-                                length -= (PGDIR_SIZE / 2);
-                        }
-                }
-
-                while (length >= SUPERSECTION_SIZE) {
-                        alloc_init_supersection(virt, virt + off, type->prot_sect);
-
-                        virt   += SUPERSECTION_SIZE;
-                        length -= SUPERSECTION_SIZE;
-                }
-        }
-
         /*
          * A section mapping covers half a "pgdir" entry.
          */