mm/hmm: remove the unused HMM_FAULT_ALLOW_RETRY flag

The HMM_FAULT_ALLOW_RETRY isn't used anywhere in the tree.  Remove it and
the weird -EAGAIN handling where handle_mm_fault() drops the mmap_sem.

Link: https://lore.kernel.org/r/20200316135310.899364-3-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/linux/hmm.h

@@ -217,11 +217,6 @@ static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
 		range->flags[HMM_PFN_VALID];
 }
 
-/*
- * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
- */
-#define HMM_FAULT_ALLOW_RETRY		(1 << 0)
-
 /* Don't fault in missing PTEs, just snapshot the current state. */
 #define HMM_FAULT_SNAPSHOT		(1 << 1)
 

mm/hmm.c

@@ -45,16 +45,10 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
 	if (!vma)
 		goto err;
 
-	if (hmm_vma_walk->flags & HMM_FAULT_ALLOW_RETRY)
-		flags |= FAULT_FLAG_ALLOW_RETRY;
 	if (write_fault)
 		flags |= FAULT_FLAG_WRITE;
 
 	ret = handle_mm_fault(vma, addr, flags);
-	if (ret & VM_FAULT_RETRY) {
-		/* Note, handle_mm_fault did up_read(&mm->mmap_sem)) */
-		return -EAGAIN;
-	}
 	if (ret & VM_FAULT_ERROR)
 		goto err;
 
@@ -662,7 +656,6 @@ static const struct mm_walk_ops hmm_walk_ops = {
  * -ENOMEM:	Out of memory.
  * -EPERM:	Invalid permission (e.g., asking for write and range is read
  *		only).
- * -EAGAIN:	A page fault needs to be retried and mmap_sem was dropped.
  * -EBUSY:	The range has been invalidated and the caller needs to wait for
  *		the invalidation to finish.
  * -EFAULT:	Invalid (i.e., either no valid vma or it is illegal to access