Re: [PATCH v3 01/15] arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary

Mike Rapoport
2024-02-08T06:11:24Z

On Mon, Jan 29, 2024 at 01:46:35PM +0100, David Hildenbrand wrote:
> From: Ryan Roberts <ryan.roberts@arm.com>
>
> Since the high bits [51:48] of an OA are not stored contiguously in the
> PTE, there is a theoretical bug in set_ptes(), which just adds PAGE_SIZE
> to the pte to get the pte with the next pfn. This works until the pfn
> crosses the 48-bit boundary, at which point we overflow into the upper
> attributes.
>
> Of course one could argue (and Matthew Wilcox has :) that we will never
> see a folio cross this boundary because we only allow naturally aligned
> power-of-2 allocation, so this would require a half-petabyte folio. So
> its only a theoretical bug. But its better that the code is robust
> regardless.
>
> I've implemented pte_next_pfn() as part of the fix, which is an opt-in
> core-mm interface. So that is now available to the core-mm, which will
> be needed shortly to support forthcoming fork()-batching optimizations.
>
> Link: https://lkml.kernel.org/r/20240125173534.1659317-1-ryan.roberts@arm.com
> Fixes: 4a169d61c2ed ("arm64: implement the new page table range API")
> Closes: https://lore.kernel.org/linux-mm/fdaeb9a5-d890-499a-92c8-d171df43ad01@arm.com/
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

> ---
> arch/arm64/include/asm/pgtable.h | 28 +++++++++++++++++-----------
> 1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index b50270107e2f..9428801c1040 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -341,6 +341,22 @@ static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages)
> mte_sync_tags(pte, nr_pages);
> }
>
> +/*
> + * Select all bits except the pfn
> + */
> +static inline pgprot_t pte_pgprot(pte_t pte)
> +{
> + unsigned long pfn = pte_pfn(pte);
> +
> + return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
> +}
> +
> +#define pte_next_pfn pte_next_pfn
> +static inline pte_t pte_next_pfn(pte_t pte)
> +{
> + return pfn_pte(pte_pfn(pte) + 1, pte_pgprot(pte));
> +}
> +
> static inline void set_ptes(struct mm_struct *mm,
> unsigned long __always_unused addr,
> pte_t *ptep, pte_t pte, unsigned int nr)
> @@ -354,7 +370,7 @@ static inline void set_ptes(struct mm_struct *mm,
> if (--nr == 0)
> break;
> ptep++;
> - pte_val(pte) += PAGE_SIZE;
> + pte = pte_next_pfn(pte);
> }
> }
> #define set_ptes set_ptes
> @@ -433,16 +449,6 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> return clear_pte_bit(pte, __pgprot(PTE_SWP_EXCLUSIVE));
> }
>
> -/*
> - * Select all bits except the pfn
> - */
> -static inline pgprot_t pte_pgprot(pte_t pte)
> -{
> - unsigned long pfn = pte_pfn(pte);
> -
> - return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
> -}
> -
> #ifdef CONFIG_NUMA_BALANCING
> /*
> * See the comment in include/linux/pgtable.h
> --
> 2.43.0
>
>

--
Sincerely yours,
Mike.