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Message-ID: <Z-VNLBWc_LThvu9k@pc636>
Date: Thu, 27 Mar 2025 14:05:48 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Uladzislau Rezki <urezki@...il.com>,
Christoph Hellwig <hch@...radead.org>,
David Hildenbrand <david@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Mark Rutland <mark.rutland@....com>,
Anshuman Khandual <anshuman.khandual@....com>,
Alexandre Ghiti <alexghiti@...osinc.com>,
Kevin Brodsky <kevin.brodsky@....com>,
linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/11] mm/vmalloc: Warn on improper use of
vunmap_range()
On Tue, Mar 04, 2025 at 03:04:37PM +0000, 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.
>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
> mm/vmalloc.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a6e7acebe9ad..fcdf67d5177a 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);
> --
> 2.43.0
>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>
--
Uladzislau Rezki
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