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From:   Alistair Popple <apopple@nvidia.com>
To:     <linux-mm@kvack.org>, <akpm@linux-foundation.org>
CC:     <nouveau@lists.freedesktop.org>, <bskeggs@redhat.com>,
        <rcampbell@nvidia.com>, <linux-doc@vger.kernel.org>,
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        <jgg@nvidia.com>, <peterx@redhat.com>, <hughd@google.com>,
        Alistair Popple <apopple@nvidia.com>
Subject: [PATCH v9 06/10] mm/memory.c: Allow different return codes for copy_nonpresent_pte()
Date:   Mon, 24 May 2021 23:27:21 +1000
Message-ID: <20210524132725.12697-7-apopple@nvidia.com>
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Currently if copy_nonpresent_pte() returns a non-zero value it is
assumed to be a swap entry which requires further processing outside the
loop in copy_pte_range() after dropping locks. This prevents other
values being returned to signal conditions such as failure which a
subsequent change requires.

Instead make copy_nonpresent_pte() return an error code if further
processing is required and read the value for the swap entry in the main
loop under the ptl.

Signed-off-by: Alistair Popple <apopple@nvidia.com>

---

v9:

New for v9 to allow device exclusive handling to occur in
copy_nonpresent_pte().
---
 mm/memory.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 2fb455c365c2..e061cfa18c11 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -718,7 +718,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
 	if (likely(!non_swap_entry(entry))) {
 		if (swap_duplicate(entry) < 0)
-			return entry.val;
+			return -EAGAIN;
 
 		/* make sure dst_mm is on swapoff's mmlist. */
 		if (unlikely(list_empty(&dst_mm->mmlist))) {
@@ -974,11 +974,13 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 			continue;
 		}
 		if (unlikely(!pte_present(*src_pte))) {
-			entry.val = copy_nonpresent_pte(dst_mm, src_mm,
-							dst_pte, src_pte,
-							src_vma, addr, rss);
-			if (entry.val)
+			ret = copy_nonpresent_pte(dst_mm, src_mm,
+						dst_pte, src_pte,
+						src_vma, addr, rss);
+			if (ret == -EAGAIN) {
+				entry = pte_to_swp_entry(*src_pte);
 				break;
+			}
 			progress += 8;
 			continue;
 		}
-- 
2.20.1