| Message ID | 20250217140809.1702789-9-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Perf improvements for hugetlb and vmalloc on arm64 | expand |
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 <anshuman.khandual@arm.com> > --- > 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);
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);
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> --- mm/vmalloc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)