[PATCH v4 6/9] 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 | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0565cbfe325c..3f98056f8c7e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -369,10 +369,12 @@ 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);
+	if (!err)
+		flush_cache_vmap(addr, end);
+
 	return err;
 }
 
@@ -758,7 +760,9 @@ 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);
-	flush_cache_vmap(addr, end);
+	if (!err)
+		flush_cache_vmap(addr, end);
+
 	return err;
 }
 
-- 
2.25.1