Subject: Re: [PATCH v4 6/9] mm/mremap: Use range flush that does TLB and page walk cache flush

From: Michael Ellerman <[email-masked]>
Date: Tue, 20 Apr 2021 13:47:50 +1000

"Aneesh Kumar K.V" <[email-masked]> writes:
> Some architectures do have the concept of page walk cache which need
> to be flush when updating higher levels of page tables. A fast mremap
> that involves moving page table pages instead of copying pte entries
> should flush page walk cache since the old translation cache is no more
> valid.
>
> Add new helper flush_pte_tlb_pwc_range() which invalidates both TLB and
> page walk cache where TLB entries are mapped with page size PAGE_SIZE.
>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/64/tlbflush.h | 11 +++++++++++
>  mm/mremap.c                                   | 15 +++++++++++++--
>  2 files changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> index f9f8a3a264f7..c236b66f490b 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> @@ -80,6 +80,17 @@ static inline void flush_hugetlb_tlb_range(struct vm_area_struct *vma,
>  	return flush_hugetlb_tlb_pwc_range(vma, start, end, false);
>  }
>  
> +#define flush_pte_tlb_pwc_range flush_tlb_pwc_range
> +static inline void flush_pte_tlb_pwc_range(struct vm_area_struct *vma,
> +					   unsigned long start, unsigned long end,
> +					   bool also_pwc)

This still uses the also_pwc name, which is a bit inconsistent with the
previous patch.

But, does it even need to be a parameter? AFAICS you always pass true,
and pwc=true is sort of implied by the name isn't it?

cheers

> +{
> +	if (radix_enabled())
> +		return radix__flush_tlb_pwc_range_psize(vma->vm_mm, start,
> +							end, mmu_virtual_psize, also_pwc);
> +	return hash__flush_tlb_range(vma, start, end);
> +}
> +
>  static inline void flush_tlb_range(struct vm_area_struct *vma,
>  				   unsigned long start, unsigned long end)
>  {
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 574287f9bb39..0e7b11daafee 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -210,6 +210,17 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
>  		drop_rmap_locks(vma);
>  }
>  
> +#ifndef flush_pte_tlb_pwc_range
> +#define flush_pte_tlb_pwc_range flush_pte_tlb_pwc_range
> +static inline void flush_pte_tlb_pwc_range(struct vm_area_struct *vma,
> +					   unsigned long start,
> +					   unsigned long end,
> +					   bool also_pwc)
> +{
> +	return flush_tlb_range(vma, start, end);
> +}
> +#endif
> +
>  #ifdef CONFIG_HAVE_MOVE_PMD
>  static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>  		  unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
> @@ -260,7 +271,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>  	VM_BUG_ON(!pmd_none(*new_pmd));
>  	pmd_populate(mm, new_pmd, (pgtable_t)pmd_page_vaddr(pmd));
>  
> -	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
> +	flush_pte_tlb_pwc_range(vma, old_addr, old_addr + PMD_SIZE, true);
>  	if (new_ptl != old_ptl)
>  		spin_unlock(new_ptl);
>  	spin_unlock(old_ptl);
> @@ -307,7 +318,7 @@ static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr,
>  	VM_BUG_ON(!pud_none(*new_pud));
>  
>  	pud_populate(mm, new_pud, (pmd_t *)pud_page_vaddr(pud));
> -	flush_tlb_range(vma, old_addr, old_addr + PUD_SIZE);
> +	flush_pte_tlb_pwc_range(vma, old_addr, old_addr + PUD_SIZE, true);
>  	if (new_ptl != old_ptl)
>  		spin_unlock(new_ptl);
>  	spin_unlock(old_ptl);
> -- 
> 2.30.2