[RFC PATCH 2/4] mm/vmalloc: undo partial mappings inside the mapping functions

[Hao Ge]

__vmap_pages_range_noflush() and friends can install some PTEs before
failing and leave them mapped, and the kernel callers do not agree on
who cleans them up. pcpu_map_pages() and kmsan_ioremap_page_range()
roll back what they mapped before the failure, while
vm_module_tags_populate() and the __GFP_NOFAIL retry loop in
__vmalloc_area_node() rely on the mapping functions cleaning up and
do not call anything like vunmap_range() themselves. When the same
range is mapped again, the attempt hits the leftovers and fails, with
a BUG() in vmap_pte_range() for huge mappings and a warning on the
small-page path.

After discussing with Suren and Ulad, we decided to put the rollback
into the entry points of the vmap API rather than into every low-level
helper. __vmap_pages_range_noflush() undoes the whole range it was
asked to map when it fails, and vmap_page_range() undoes its range
for the ioremap-style mappings.

The rollback is __vunmap_range_noflush(), it only clears the PTEs,
no TLB flush, nothing has touched these mappings.
vmap_pages_range_noflush() drops the KMSAN metadata when the data
mapping fails, and an empty range bails out with -EINVAL now, which
used to BUG_ON() on the small-page path and map nothing at all on
the huge-page one.

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Suggested-by: Uladyslau Rezki <urezki@xxxxxxxxx>
Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>
---
 mm/vmalloc.c | 44 ++++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 12 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index db669103dc66..e1b376f57dd2 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -363,6 +363,9 @@ int vmap_page_range(unsigned long addr, unsigned long end,
 	if (!err)
 		err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
 					       ioremap_max_page_shift);
+	if (err)
+		__vunmap_range_noflush(addr, end);
+
 	return err;
 }
 
@@ -683,27 +686,35 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
 		pgprot_t prot, struct page **pages, unsigned int page_shift)
 {
 	unsigned int i, nr = (end - addr) >> PAGE_SHIFT;
+	unsigned long start = addr;
+	int err = 0;
+
+	if (WARN_ON_ONCE(addr >= end))
+		return -EINVAL;
 
 	if (WARN_ON_ONCE(page_shift < PAGE_SHIFT))
 		return -EINVAL;
 
 	if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
-			page_shift == PAGE_SHIFT)
-		return vmap_small_pages_range_noflush(addr, end, prot, pages);
-
-	for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
-		int err;
-
-		err = vmap_range_noflush(addr, addr + (1UL << page_shift),
+			page_shift == PAGE_SHIFT) {
+		err = vmap_small_pages_range_noflush(addr, end, prot, pages);
+	} else {
+		for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
+			err = vmap_range_noflush(addr, addr + (1UL << page_shift),
 					page_to_phys(pages[i]), prot,
 					page_shift);
-		if (err)
-			return err;
+			if (err)
+				break;
 
-		addr += 1UL << page_shift;
+			addr += 1UL << page_shift;
+		}
 	}
 
-	return 0;
+	/* Undo the PTEs installed before the failure. */
+	if (err)
+		__vunmap_range_noflush(start, end);
+
+	return err;
 }
 
 int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
@@ -715,7 +726,16 @@ int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
 
 	if (ret)
 		return ret;
-	return __vmap_pages_range_noflush(addr, end, prot, pages, page_shift);
+
+	ret = __vmap_pages_range_noflush(addr, end, prot, pages, page_shift);
+	/*
+	 * The page tables undo themselves on failure. Tear down the
+	 * metadata that was fully set up before the mapping failed.
+	 */
+	if (ret)
+		kmsan_vunmap_range_noflush(addr, end);
+
+	return ret;
 }
 
 static int __vmap_pages_range(unsigned long addr, unsigned long end,
-- 
2.25.1