linux-kernel - Re: [PATCH v3] arm64: Restrict pagetable teardown to avoid false warning

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Message-ID: <914071fe-c133-4c9d-bb2d-9b9fca8a1798@arm.com>
Date: Fri, 30 May 2025 09:25:05 +0530
From: Dev Jain <dev.jain@....com>
To: catalin.marinas@....com, will@...nel.org
Cc: david@...hat.com, ryan.roberts@....com, anshuman.khandual@....com,
 mark.rutland@....com, yang@...amperecomputing.com,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v3] arm64: Restrict pagetable teardown to avoid false
 warning


On 27/05/25 1:56 pm, Dev Jain wrote:
> Commit 9c006972c3fe removes the pxd_present() checks because the caller
> checks pxd_present(). But, in case of vmap_try_huge_pud(), the caller only
> checks pud_present(); pud_free_pmd_page() recurses on each pmd through
> pmd_free_pte_page(), wherein the pmd may be none. Thus it is possible to
> hit a warning in the latter, since pmd_none => !pmd_table(). Thus, add
> a pmd_present() check in pud_free_pmd_page().
>
> This problem was found by code inspection.
>
> Fixes: 9c006972c3fe (arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table())

I missed double quotes around the fixes commit message. Can Will or Catalin fix that,
or shall I resend.

> Cc: <stable@...r.kernel.org>
> Reported-by: Ryan Roberts <ryan.roberts@....com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> This patch is based on 6.15-rc6.
>
> v2->v3:
>   - Use pmdp_get()
>
> v1->v2:
>   - Enforce check in caller
>
>   arch/arm64/mm/mmu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ea6695d53fb9..5a9bf291c649 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1286,7 +1286,8 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
>   	next = addr;
>   	end = addr + PUD_SIZE;
>   	do {
> -		pmd_free_pte_page(pmdp, next);
> +		if (pmd_present(pmdp_get(pmdp)))
> +			pmd_free_pte_page(pmdp, next);
>   	} while (pmdp++, next += PMD_SIZE, next != end);
>   
>   	pud_clear(pudp);