x86/mm: Introduce lookup_address_in_mm()

Add a helper, lookup_address_in_mm(), to traverse the page tables of a
given mm struct.  KVM will use the helper to retrieve the host mapping
level, e.g. 4k vs. 2mb vs. 1gb, of a compound (or DAX-backed) page
without having to resort to implementation specific metadata.  E.g. KVM
currently uses different logic for HugeTLB vs. THP, and would add a
third variant for DAX-backed files.

Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 1b99ad05b117..2c70a8b20b04 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -618,6 +618,17 @@ pte_t *lookup_address(unsigned long address, unsigned int *level)
 }
 EXPORT_SYMBOL_GPL(lookup_address);
 
+/*
+ * Lookup the page table entry for a virtual address in a given mm. Return a
+ * pointer to the entry and the level of the mapping.
+ */
+pte_t *lookup_address_in_mm(struct mm_struct *mm, unsigned long address,
+			    unsigned int *level)
+{
+	return lookup_address_in_pgd(pgd_offset(mm, address), address, level);
+}
+EXPORT_SYMBOL_GPL(lookup_address_in_mm);
+
 static pte_t *_lookup_address_cpa(struct cpa_data *cpa, unsigned long address,
 				  unsigned int *level)
 {