Re: [PATCH v2 08/14] mm/vmalloc: Warn on improper use of vunmap_range()
From: Anshuman Khandual <hidden>
Date: 2025-02-20 07:02:55
Also in:
linux-mm, lkml
On 2/17/25 19:38, Ryan Roberts wrote:
A call to vmalloc_huge() may cause memory blocks to be mapped at pmd or pud level. But it is possible to subsequently call vunmap_range() on a sub-range of the mapped memory, which partially overlaps a pmd or pud. In this case, vmalloc unmaps the entire pmd or pud so that the no-overlapping portion is also unmapped. Clearly that would have a bad outcome, but it's not something that any callers do today as far as I can tell. So I guess it's just expected that callers will not do this. However, it would be useful to know if this happened in future; let's add a warning to cover the eventuality. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
LGTM and stands on its own independent of the series here. Reviewed-by: Anshuman Khandual <redacted>
quoted hunk ↗ jump to hunk
--- mm/vmalloc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 61981ee1c9d2..a7e34e6936d2 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c@@ -374,8 +374,10 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, if (cleared || pmd_bad(*pmd)) *mask |= PGTBL_PMD_MODIFIED; - if (cleared) + if (cleared) { + WARN_ON(next - addr < PMD_SIZE); continue; + } if (pmd_none_or_clear_bad(pmd)) continue; vunmap_pte_range(pmd, addr, next, mask);@@ -399,8 +401,10 @@ static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, if (cleared || pud_bad(*pud)) *mask |= PGTBL_PUD_MODIFIED; - if (cleared) + if (cleared) { + WARN_ON(next - addr < PUD_SIZE); continue; + } if (pud_none_or_clear_bad(pud)) continue; vunmap_pmd_range(pud, addr, next, mask);