mm: Introduce untagged_addr_remote()

untagged_addr() removes tags/metadata from the address and brings it to
the canonical form. The helper is implemented on arm64 and sparc. Both of
them do untagging based on global rules.

However, Linear Address Masking (LAM) on x86 introduces per-process
settings for untagging. As a result, untagged_addr() is now only
suitable for untagging addresses for the current proccess.

The new helper untagged_addr_remote() has to be used when the address
targets remote process. It requires the mmap lock for target mm to be
taken.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/all/20230312112612.31869-6-kirill.shutemov%40linux.intel.com

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/gup.c b/mm/gup.c
index eab18ba045db..5ee8b682a0fe 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1085,7 +1085,7 @@ static long __get_user_pages(struct mm_struct *mm,
 	if (!nr_pages)
 		return 0;
 
-	start = untagged_addr(start);
+	start = untagged_addr_remote(mm, start);
 
 	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
@@ -1259,7 +1259,7 @@ int fixup_user_fault(struct mm_struct *mm,
 	struct vm_area_struct *vma;
 	vm_fault_t ret;
 
-	address = untagged_addr(address);
+	address = untagged_addr_remote(mm, address);
 
 	if (unlocked)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;