ARM: mm: HugeTLB support for non-LPAE systems.

Based on Bill Carson's HugeTLB patch, with the big difference being
in the way PTEs are passed back to the memory manager. Rather than
store a "Linux Huge PTE" separately; we make one up on the fly in
huge_ptep_get. Also rather than consider 16M supersections, we focus
solely on 2x1M sections.

To construct a huge PTE on the fly we need additional information
(such as the accessed flag and dirty bit) which we choose to store
in the domain bits of the short section descriptor. In order to use
these domain bits for storage, we need to make ourselves a client
for all 16 domains and this is done in head.S.

Storing extra information in the domain bits also makes it a lot
easier to implement Transparent Huge Pages, and some of the code in
pgtable-2level.h is arranged to facilitate THP support in a later
patch.

Non-LPAE HugeTLB pages are incompatible with the huge page migration
code (enabled when CONFIG_MEMORY_FAILURE is selected) as that code
dereferences PTEs directly, rather than calling huge_ptep_get and
set_huge_pte_at.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>

1 files changed, 121 insertions, 0 deletions

diff --git a/arch/arm/include/asm/hugetlb-2level.h b/arch/arm/include/asm/hugetlb-2level.h
new file mode 100644
index 000000000000..eb0e8b684a00
--- /dev/null
+++ b/arch/arm/include/asm/hugetlb-2level.h
@@ -0,0 +1,121 @@
+/*
+ * arch/arm/include/asm/hugetlb-2level.h
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * Based on arch/x86/include/asm/hugetlb.h and Bill Carson's patches
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef _ASM_ARM_HUGETLB_2LEVEL_H
+#define _ASM_ARM_HUGETLB_2LEVEL_H
+
+
+static inline pte_t huge_ptep_get(pte_t *ptep)
+{
+	pmd_t pmd =  *((pmd_t *)ptep);
+	pte_t retval;
+
+	if (!pmd_val(pmd))
+		return __pte(0);
+
+	retval = __pte((pteval_t) (pmd_val(pmd) & HPAGE_MASK)
+			| arm_hugepteprotval);
+
+	if (pmd_exec(pmd))
+		retval = pte_mkexec(retval);
+	else
+		retval = pte_mknexec(retval);
+
+	if (pmd_young(pmd))
+		retval = pte_mkyoung(retval);
+	else
+		retval = pte_mkold(retval);
+
+	if (pmd_dirty(pmd))
+		retval = pte_mkdirty(retval);
+	else
+		retval = pte_mkclean(retval);
+
+	if (pmd_write(pmd))
+		retval = pte_mkwrite(retval);
+	else
+		retval = pte_wrprotect(retval);
+
+	return retval;
+}
+
+static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
+				   pte_t *ptep, pte_t pte)
+{
+	pmdval_t pmdval = (pmdval_t) pte_val(pte);
+	pmd_t *pmdp = (pmd_t *) ptep;
+
+	/* take the target address bits from the pte only */
+	pmdval &= HPAGE_MASK;
+
+	/*
+	 * now use pmd_modify to translate the permission bits from the pte
+	 * and set the memory type information.
+	 */
+	pmdval = pmd_val(pmd_modify(__pmd(pmdval), __pgprot(pte_val(pte))));
+
+	__sync_icache_dcache(pte);
+
+	set_pmd_at(mm, addr, pmdp, __pmd(pmdval));
+}
+
+static inline pte_t pte_mkhuge(pte_t pte) { return pte; }
+
+static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
+					 unsigned long addr, pte_t *ptep)
+{
+	pmd_t *pmdp = (pmd_t *)ptep;
+	pmd_clear(pmdp);
+	flush_tlb_range(vma, addr, addr + HPAGE_SIZE);
+}
+
+static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
+					   unsigned long addr, pte_t *ptep)
+{
+	pmd_t *pmdp = (pmd_t *) ptep;
+	set_pmd_at(mm, addr, pmdp, pmd_wrprotect(*pmdp));
+}
+
+
+static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
+					    unsigned long addr, pte_t *ptep)
+{
+	pmd_t *pmdp = (pmd_t *)ptep;
+	pte_t pte = huge_ptep_get(ptep);
+	pmd_clear(pmdp);
+
+	return pte;
+}
+
+static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
+					     unsigned long addr, pte_t *ptep,
+					     pte_t pte, int dirty)
+{
+	int changed = !pte_same(huge_ptep_get(ptep), pte);
+	if (changed) {
+		set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
+		flush_tlb_range(vma, addr, addr + HPAGE_SIZE);
+	}
+
+	return changed;
+}
+
+#endif /* _ASM_ARM_HUGETLB_2LEVEL_H */