x86: Introduce function to get pmd entry pointer

Introduces lookup_pmd_address() to get the address of the pmd entry
related to a virtual address in the current address space. This
function is needed for support of a virtual mapped sparse p2m list
in xen pv domains, as we need the address of the pmd entry, not the
one of the pte in that case.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 36de293caf25..129810887e83 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -384,6 +384,26 @@ static pte_t *_lookup_address_cpa(struct cpa_data *cpa, unsigned long address,
 }
 
 /*
+ * Lookup the PMD entry for a virtual address. Return a pointer to the entry
+ * or NULL if not present.
+ */
+pmd_t *lookup_pmd_address(unsigned long address)
+{
+        pgd_t *pgd;
+        pud_t *pud;
+
+        pgd = pgd_offset_k(address);
+        if (pgd_none(*pgd))
+                return NULL;
+
+        pud = pud_offset(pgd, address);
+        if (pud_none(*pud) || pud_large(*pud) || !pud_present(*pud))
+                return NULL;
+
+        return pmd_offset(pud, address);
+}
+
+/*
  * This is necessary because __pa() does not work on some
  * kinds of memory, like vmalloc() or the alloc_remap()
  * areas on 32-bit NUMA systems.  The percpu areas can