Re: [RFC PATCH v2 05/19] x86, mm: Use cache of page tables

[Mike Rapoport]

On Mon, Aug 30, 2021 at 04:59:13PM -0700, Rick Edgecombe wrote:
> Change the page table allocation functions defined in pgalloc.h to use
> a cache of physically grouped pages. This will let the page tables be set
> with PKS permissions later.
> 
> For userspace page tables, they are gathered up using mmu gather, and
> freed along with other types of pages in swap.c. Move setting/clearing of
> the PageTable page flag to the allocators so that swap can know to return
> this page to the cache of page tables, and not free it to the page
> allocator. Where it currently is, in the ctor/dtors, causes it to be
> cleared before the page gets to swap.
> 
> Do not set PKS permissions on the page tables, because the page table
> setting functions cannot handle it yet. This will be done in later
> patches.
> 
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
>  arch/x86/include/asm/pgalloc.h |  6 ++-
>  arch/x86/include/asm/pgtable.h |  6 +++
>  arch/x86/mm/pgtable.c          | 79 ++++++++++++++++++++++++++++++++++
>  include/asm-generic/pgalloc.h  | 44 ++++++++++++++-----
>  include/linux/mm.h             | 11 +++--
>  mm/swap.c                      |  6 +++
>  mm/swap_state.c                |  5 +++
>  7 files changed, 142 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
> index c7ec5bb88334..1ff308ea76cd 100644
> --- a/arch/x86/include/asm/pgalloc.h
> +++ b/arch/x86/include/asm/pgalloc.h
> @@ -7,6 +7,10 @@
>  #include <linux/pagemap.h>
>  
>  #define __HAVE_ARCH_PTE_ALLOC_ONE
> +#ifdef CONFIG_PKS_PG_TABLES
> +#define __HAVE_ARCH_FREE_TABLE
> +#define __HAVE_ARCH_ALLOC_TABLE

I think one define would suffice. If we'd ever have an architecture that
can implement only one of those, we update the ifdefery in
asm-generic/pgalloc.h

> +#endif
>  #define __HAVE_ARCH_PGD_FREE
>  #include <asm-generic/pgalloc.h>
>  
> @@ -162,7 +166,7 @@ static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
>  		return;
>  
>  	BUG_ON((unsigned long)p4d & (PAGE_SIZE-1));
> -	free_page((unsigned long)p4d);
> +	free_table(virt_to_page(p4d));
>  }
>  
>  extern void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d);

...

> diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h
> index 02932efad3ab..e576c19abc8c 100644
> --- a/include/asm-generic/pgalloc.h
> +++ b/include/asm-generic/pgalloc.h
> @@ -2,11 +2,26 @@
>  #ifndef __ASM_GENERIC_PGALLOC_H
>  #define __ASM_GENERIC_PGALLOC_H
>  
> +#include <linux/mm.h>
> +

Why is this required?

>  #ifdef CONFIG_MMU
>  
>  #define GFP_PGTABLE_KERNEL	(GFP_KERNEL | __GFP_ZERO)
>  #define GFP_PGTABLE_USER	(GFP_PGTABLE_KERNEL | __GFP_ACCOUNT)
>  
> +#ifndef __HAVE_ARCH_ALLOC_TABLE
> +static inline struct page *alloc_table(gfp_t gfp)
> +{
> +	return alloc_page(gfp);
> +}
> +#else /* __HAVE_ARCH_ALLOC_TABLE */
> +extern struct page *alloc_table(gfp_t gfp);
> +#endif /* __HAVE_ARCH_ALLOC_TABLE */
> +
> +#ifdef __HAVE_ARCH_FREE_TABLE
> +extern void free_table(struct page *);
> +#endif /* __HAVE_ARCH_FREE_TABLE */
> +
>  /**
>   * __pte_alloc_one_kernel - allocate a page for PTE-level kernel page table
>   * @mm: the mm_struct of the current context

...

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c13c7af7cad3..ab63d5a201cb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2327,6 +2327,13 @@ static inline bool ptlock_init(struct page *page) { return true; }
>  static inline void ptlock_free(struct page *page) {}
>  #endif /* USE_SPLIT_PTE_PTLOCKS */
>  
> +#ifndef CONFIG_PKS_PG_TABLES
> +static inline void free_table(struct page *table_page)
> +{
> +	__free_pages(table_page, 0);
> +}
> +#endif /* CONFIG_PKS_PG_TABLES */
> +

Can't this live in asm-generic/pgalloc.h?
Then you won't need to include linux/mm.h there.

>  static inline void pgtable_init(void)
>  {
>  	ptlock_cache_init();
> @@ -2337,7 +2344,6 @@ static inline bool pgtable_pte_page_ctor(struct page *page)
>  {
>  	if (!ptlock_init(page))
>  		return false;
> -	__SetPageTable(page);

This change is only valid when __HAVE_ARCH_ALLOC_TABLE is set.

>  	inc_lruvec_page_state(page, NR_PAGETABLE);
>  	return true;
>  }
> @@ -2345,7 +2351,6 @@ static inline bool pgtable_pte_page_ctor(struct page *page)
>  static inline void pgtable_pte_page_dtor(struct page *page)
>  {
>  	ptlock_free(page);
> -	__ClearPageTable(page);
>  	dec_lruvec_page_state(page, NR_PAGETABLE);
>  }
>  

-- 
Sincerely yours,
Mike.