Re: [PATCHv1, RFC 5/8] x86/mm: Fold p4d page table layer at runtime

[Brian Gerst]

On Thu, May 25, 2017 at 4:33 PM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> This patch changes page table helpers to fold p4d at runtime.
> The logic is the same as in <asm-generic/pgtable-nop4d.h>.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/paravirt.h |  3 ++-
>  arch/x86/include/asm/pgalloc.h  |  5 ++++-
>  arch/x86/include/asm/pgtable.h  | 10 +++++++++-
>  3 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 55fa56fe4e45..e934ed6dc036 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -615,7 +615,8 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
>
>  static inline void pgd_clear(pgd_t *pgdp)
>  {
> -       set_pgd(pgdp, __pgd(0));
> +       if (!p4d_folded)
> +               set_pgd(pgdp, __pgd(0));
>  }
>
>  #endif  /* CONFIG_PGTABLE_LEVELS == 5 */
> diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
> index b2d0cd8288aa..5c42262169d0 100644
> --- a/arch/x86/include/asm/pgalloc.h
> +++ b/arch/x86/include/asm/pgalloc.h
> @@ -155,6 +155,8 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
>  #if CONFIG_PGTABLE_LEVELS > 4
>  static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d)
>  {
> +       if (p4d_folded)
> +               return;
>         paravirt_alloc_p4d(mm, __pa(p4d) >> PAGE_SHIFT);
>         set_pgd(pgd, __pgd(_PAGE_TABLE | __pa(p4d)));
>  }
> @@ -179,7 +181,8 @@ extern void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d);
>  static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
>                                   unsigned long address)
>  {
> -       ___p4d_free_tlb(tlb, p4d);
> +       if (!p4d_folded)
> +               ___p4d_free_tlb(tlb, p4d);
>  }
>
>  #endif /* CONFIG_PGTABLE_LEVELS > 4 */
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 77037b6f1caa..4516a1bdcc31 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -53,7 +53,7 @@ extern struct mm_struct *pgd_page_get_mm(struct page *page);
>
>  #ifndef __PAGETABLE_P4D_FOLDED
>  #define set_pgd(pgdp, pgd)             native_set_pgd(pgdp, pgd)
> -#define pgd_clear(pgd)                 native_pgd_clear(pgd)
> +#define pgd_clear(pgd)                 (!p4d_folded ? native_pgd_clear(pgd) : 0)
>  #endif
>
>  #ifndef set_p4d
> @@ -847,6 +847,8 @@ static inline unsigned long p4d_index(unsigned long address)
>  #if CONFIG_PGTABLE_LEVELS > 4
>  static inline int pgd_present(pgd_t pgd)
>  {
> +       if (p4d_folded)
> +               return 1;
>         return pgd_flags(pgd) & _PAGE_PRESENT;
>  }
>
> @@ -864,16 +866,22 @@ static inline unsigned long pgd_page_vaddr(pgd_t pgd)
>  /* to find an entry in a page-table-directory. */
>  static inline p4d_t *p4d_offset(pgd_t *pgd, unsigned long address)
>  {
> +       if (p4d_folded)
> +               return (p4d_t *)pgd;
>         return (p4d_t *)pgd_page_vaddr(*pgd) + p4d_index(address);
>  }
>
>  static inline int pgd_bad(pgd_t pgd)
>  {
> +       if (p4d_folded)
> +               return 0;
>         return (pgd_flags(pgd) & ~_PAGE_USER) != _KERNPG_TABLE;
>  }
>
>  static inline int pgd_none(pgd_t pgd)
>  {
> +       if (p4d_folded)
> +               return 0;
>         /*
>          * There is no need to do a workaround for the KNL stray
>          * A/D bit erratum here.  PGDs only point to page tables

These should use static_cpu_has(X86_FEATURE_LA57), so that it gets
patched by alternatives.

--
Brian Gerst