Hi Uladzislau and Suren On 2026/10/14 00:39, Uladzislau Rezki wrote: > On Tue, Oct 13, 2026 at 03:23:14PM +0400, Suren Baghdasaryan wrote: >> On Fri, Oct 9, 2026 at 10:36 AM Hao Ge <[email protected]> wrote: >>> >>> __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 <[email protected]> >>> Suggested-by: Uladyslau Rezki <[email protected]> >>> Signed-off-by: Hao Ge <[email protected]> >>> --- >>> 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); >> >> Would it be too complicated to track how much was actually mapped and >> unmap only that portion? >> > I think it is possible to vunmap the range which is already unmapped. > i.e. in this case it is better to no to track anything as soon as a > mapping failure is a corner case. Also it is more reliable without > extra track logic.
Thank you both. I take note of Suren's concerns. The worst case is a single PMD where only the first page was installed, __vunmap_range_noflush() then loops 512 times to undo one PTE, plus 511 empty ones. And tracking the exact progress would require vmap_pages_p4d/pud/pmd_range() to report how far they got. That also puts counting instructions on the successful mapping path, while the saving only pays off on the failure one. So I agree with Ulad. Thanks Best Regards Hao > > -- > Uladzislau Rezki
