[PATCH v3 07/10] mm/vmalloc: only flush the cache after the vmap succeeded

[Hao Ge]

vmap_page_range() and __vmap_pages_range() call flush_cache_vmap()
before they even look at the error code. A failed mapping is never
used, so the flush is pointless at best.

According to the Sashiko review it is worse than pointless on UML:
flush_cache_vmap() there is flush_tlb_kernel_range(), which syncs the
PTEs into the host OS. Flushing a half-installed mapping therefore
leaves host mappings behind for a range that was just freed again.

Only flush when the mapping, and for vmap_page_range() also the KMSAN
metadata, is fully set up.

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>
---
 mm/vmalloc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4d74144dfaff..96e15d6cfc6d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -359,11 +359,14 @@ int vmap_page_range(unsigned long addr, unsigned long end,
 
 	err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
 				 ioremap_max_page_shift);
-	flush_cache_vmap(addr, end);
 	if (!err)
 		err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
 					       ioremap_max_page_shift);
-	return err;
+	if (err)
+		return err;
+
+	flush_cache_vmap(addr, end);
+	return 0;
 }
 
 int ioremap_page_range(unsigned long addr, unsigned long end,
@@ -745,8 +748,11 @@ static int __vmap_pages_range(unsigned long addr, unsigned long end,
 	int err;
 
 	err = vmap_pages_range_noflush(addr, end, prot, pages, page_shift, gfp_mask);
+	if (err)
+		return err;
+
 	flush_cache_vmap(addr, end);
-	return err;
+	return 0;
 }
 
 /**
-- 
2.25.1