x86: PAT: add follow_pfnmp_pte routine to help tracking pfnmap pages - v3

Impact: New currently unused interface.

Add a generic interface to follow pfn in a pfnmap vma range. This is used by
one of the subsequent x86 PAT related patch to keep track of memory types
for vma regions across vma copy and free.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index cef95c8c77fa..8ca6bbf34ad6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1111,6 +1111,49 @@ no_page_table:
         return page;
 }
 
+int follow_pfnmap_pte(struct vm_area_struct *vma, unsigned long address,
+                        pte_t *ret_ptep)
+{
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        pte_t *ptep, pte;
+        spinlock_t *ptl;
+        struct page *page;
+        struct mm_struct *mm = vma->vm_mm;
+
+        if (!is_pfn_mapping(vma))
+                goto err;
+
+        page = NULL;
+        pgd = pgd_offset(mm, address);
+        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+                goto err;
+
+        pud = pud_offset(pgd, address);
+        if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+                goto err;
+
+        pmd = pmd_offset(pud, address);
+        if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+                goto err;
+
+        ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+
+        pte = *ptep;
+        if (!pte_present(pte))
+                goto err_unlock;
+
+        *ret_ptep = pte;
+        pte_unmap_unlock(ptep, ptl);
+        return 0;
+
+err_unlock:
+        pte_unmap_unlock(ptep, ptl);
+err:
+        return -EINVAL;
+}
+
 /* Can we do the FOLL_ANON optimization? */
 static inline int use_zero_page(struct vm_area_struct *vma)
 {