fsi: Add regmap and refactor sbefifo

Merge series from Eddie James <eajames@linux.ibm.com>:

The SBEFIFO hardware can now be attached over a new I2C endpoint interface
called the I2C Responder (I2CR). In order to use the existing SBEFIFO
driver, add a regmap driver for the FSI bus and an endpoint driver for the
I2CR. Then, refactor the SBEFIFO and OCC drivers to clean up and use the
new regmap driver or the I2CR interface.

This branch just has the regmap change so it can be shared with the FSI
code.

1 files changed, 22 insertions, 5 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e24e8a47ce8a..650ab6cfd5f4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -64,7 +64,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
 	pte_t _dst_pte, *dst_pte;
 	bool writable = dst_vma->vm_flags & VM_WRITE;
 	bool vm_shared = dst_vma->vm_flags & VM_SHARED;
-	bool page_in_cache = page->mapping;
+	bool page_in_cache = page_mapping(page);
 	spinlock_t *ptl;
 	struct inode *inode;
 	pgoff_t offset, max_off;
@@ -157,11 +157,28 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 		if (!page)
 			goto out;
 
-		page_kaddr = kmap_atomic(page);
+		page_kaddr = kmap_local_page(page);
+		/*
+		 * The read mmap_lock is held here.  Despite the
+		 * mmap_lock being read recursive a deadlock is still
+		 * possible if a writer has taken a lock.  For example:
+		 *
+		 * process A thread 1 takes read lock on own mmap_lock
+		 * process A thread 2 calls mmap, blocks taking write lock
+		 * process B thread 1 takes page fault, read lock on own mmap lock
+		 * process B thread 2 calls mmap, blocks taking write lock
+		 * process A thread 1 blocks taking read lock on process B
+		 * process B thread 1 blocks taking read lock on process A
+		 *
+		 * Disable page faults to prevent potential deadlock
+		 * and retry the copy outside the mmap_lock.
+		 */
+		pagefault_disable();
 		ret = copy_from_user(page_kaddr,
 				     (const void __user *) src_addr,
 				     PAGE_SIZE);
-		kunmap_atomic(page_kaddr);
+		pagefault_enable();
+		kunmap_local(page_kaddr);
 
 		/* fallback to copy_from_user outside mmap_lock */
 		if (unlikely(ret)) {
@@ -646,11 +663,11 @@ retry:
 			mmap_read_unlock(dst_mm);
 			BUG_ON(!page);
 
-			page_kaddr = kmap(page);
+			page_kaddr = kmap_local_page(page);
 			err = copy_from_user(page_kaddr,
 					     (const void __user *) src_addr,
 					     PAGE_SIZE);
-			kunmap(page);
+			kunmap_local(page_kaddr);
 			if (unlikely(err)) {
 				err = -EFAULT;
 				goto out;