[RFC 05/11] mm: add follow_pte_pmd()

Ross Zwisler
2015-10-29T20:12:37Z

Similar to follow_pte(), follow_pte_pmd() allows either a PTE leaf or a
huge page PMD leaf to be found and returned.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
include/linux/mm.h | 2 ++
mm/memory.c | 41 +++++++++++++++++++++++++++++++++--------
2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80001de..393441c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1166,6 +1166,8 @@ int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
struct vm_area_struct *vma);
void unmap_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen, int even_cows);
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+ pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
unsigned long *pfn);
int follow_phys(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index deb679c..c2b8c0a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3512,8 +3512,8 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
}
#endif /* __PAGETABLE_PMD_FOLDED */

-static int __follow_pte(struct mm_struct *mm, unsigned long address,
- pte_t **ptepp, spinlock_t **ptlp)
+static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+ pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
{
pgd_t *pgd;
pud_t *pud;
@@ -3529,12 +3529,23 @@ static int __follow_pte(struct mm_struct *mm, unsigned long address,
goto out;

pmd = pmd_offset(pud, address);
- VM_BUG_ON(pmd_trans_huge(*pmd));
- if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
- goto out;

- /* We cannot handle huge page PFN maps. Luckily they don't exist. */
- if (pmd_huge(*pmd))
+ if (pmd_huge(*pmd)) {
+ if (!pmdpp)
+ goto out;
+
+ *ptlp = pmd_lock(mm, pmd);
+ if (pmd_huge(*pmd)) {
+ /* Success, we found a large PTE */
+ *pmdpp = pmd;
+ return 0;
+ }
+ /* Somebody removed the PMD entry, try it as a pte */
+ spin_unlock(*ptlp);
+ }
+
+ /* FIXME: pmd_bad() is sometimes set for DAX pmds? */
+ if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
goto out;

ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
@@ -3557,9 +3568,23 @@ static inline int follow_pte(struct mm_struct *mm, unsigned long address,

/* (void) is needed to make gcc happy */
(void) __cond_lock(*ptlp,
- !(res = __follow_pte(mm, address, ptepp, ptlp)));
+ !(res = __follow_pte_pmd(mm, address, ptepp, NULL,
+ ptlp)));
+ return res;
+}
+
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+ pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+ int res;
+
+ /* (void) is needed to make gcc happy */
+ (void) __cond_lock(*ptlp,
+ !(res = __follow_pte_pmd(mm, address, ptepp, pmdpp,
+ ptlp)));
return res;
}
+EXPORT_SYMBOL(follow_pte_pmd);

/**
* follow_pfn - look up PFN at a user virtual address
--
2.1.0