Re: [PATCH v1 2/3] mm/hugetlb: enforce that PMD PT sharing has split PMD PT locks

[Mike Rapoport <rppt@kernel.org>]

On Fri, Jul 26, 2024 at 05:07:27PM +0200, David Hildenbrand wrote:
> Sharing page tables between processes but falling back to per-MM page
> table locks cannot possibly work.
> 
> So, let's make sure that we do have split PMD locks by adding a new
> Kconfig option and letting that depend on CONFIG_SPLIT_PMD_PTLOCKS.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  fs/Kconfig              | 4 ++++
>  include/linux/hugetlb.h | 5 ++---
>  mm/hugetlb.c            | 8 ++++----
>  3 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/Kconfig b/fs/Kconfig
> index a46b0cbc4d8f6..0e4efec1d92e6 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -288,6 +288,10 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>  	depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
>  	depends on SPARSEMEM_VMEMMAP
>  
> +config HUGETLB_PMD_PAGE_TABLE_SHARING
> +	def_bool HUGETLB_PAGE
> +	depends on ARCH_WANT_HUGE_PMD_SHARE && SPLIT_PMD_PTLOCKS
> +
>  config ARCH_HAS_GIGANTIC_PAGE
>  	bool
>  
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index da800e56fe590..4d2f3224ff027 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -1243,7 +1243,7 @@ static inline __init void hugetlb_cma_reserve(int order)
>  }
>  #endif
>  
> -#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
>  static inline bool hugetlb_pmd_shared(pte_t *pte)
>  {
>  	return page_count(virt_to_page(pte)) > 1;
> @@ -1279,8 +1279,7 @@ bool __vma_private_lock(struct vm_area_struct *vma);
>  static inline pte_t *
>  hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz)
>  {
> -#if defined(CONFIG_HUGETLB_PAGE) && \
> -	defined(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && defined(CONFIG_LOCKDEP)
> +#if defined(CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING) && defined(CONFIG_LOCKDEP)
>  	struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
>  
>  	/*
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0858a18272073..c4d94e122c41f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -7211,7 +7211,7 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
>  	return 0;
>  }
>  
> -#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
>  static unsigned long page_table_shareable(struct vm_area_struct *svma,
>  				struct vm_area_struct *vma,
>  				unsigned long addr, pgoff_t idx)
> @@ -7373,7 +7373,7 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
>  	return 1;
>  }
>  
> -#else /* !CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
> +#else /* !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */
>  
>  pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
>  		      unsigned long addr, pud_t *pud)
> @@ -7396,7 +7396,7 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr)
>  {
>  	return false;
>  }
> -#endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
> +#endif /* CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */
>  
>  #ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
>  pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> @@ -7494,7 +7494,7 @@ unsigned long hugetlb_mask_last_page(struct hstate *h)
>  /* See description above.  Architectures can provide their own version. */
>  __weak unsigned long hugetlb_mask_last_page(struct hstate *h)
>  {
> -#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
>  	if (huge_page_size(h) == PMD_SIZE)
>  		return PUD_SIZE - PMD_SIZE;
>  #endif
> -- 
> 2.45.2
> 
> 

-- 
Sincerely yours,
Mike.