On Wed, Oct 14, 2026 at 11:28 AM Hao Ge <[email protected]> wrote: > > 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.
Got it. Makes sense. > > Thanks > Best Regards > Hao > > > > > -- > > Uladzislau Rezki
