linux-kernel - Re: [PATCH v5 05/17] arm64: pgtable: use mmu gather to free p4d level page table

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Message-ID: <20250113162600.GA14101@willie-the-truck>
Date: Mon, 13 Jan 2025 16:26:01 +0000
From: Will Deacon <will@...nel.org>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: peterz@...radead.org, agordeev@...ux.ibm.com, kevin.brodsky@....com,
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Subject: Re: [PATCH v5 05/17] arm64: pgtable: use mmu gather to free p4d
 level page table

On Wed, Jan 08, 2025 at 02:57:21PM +0800, Qi Zheng wrote:
> Like other levels of page tables, also use mmu gather mechanism to free
> p4d level page table.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Originally-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Kevin Brodsky <kevin.brodsky@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
>  arch/arm64/include/asm/pgalloc.h |  1 -
>  arch/arm64/include/asm/tlb.h     | 14 ++++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
> index 2965f5a7e39e3..1b4509d3382c6 100644
> --- a/arch/arm64/include/asm/pgalloc.h
> +++ b/arch/arm64/include/asm/pgalloc.h
> @@ -85,7 +85,6 @@ static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>  	__pgd_populate(pgdp, __pa(p4dp), pgdval);
>  }
>  
> -#define __p4d_free_tlb(tlb, p4d, addr)  p4d_free((tlb)->mm, p4d)
>  #else
>  static inline void __pgd_populate(pgd_t *pgdp, phys_addr_t p4dp, pgdval_t prot)
>  {
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index a947c6e784ed2..445282cde9afb 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -111,4 +111,18 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pudp,
>  }
>  #endif
>  
> +#if CONFIG_PGTABLE_LEVELS > 4
> +static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4dp,
> +				  unsigned long addr)
> +{
> +	struct ptdesc *ptdesc = virt_to_ptdesc(p4dp);
> +
> +	if (!pgtable_l5_enabled())
> +		return;
> +
> +	pagetable_p4d_dtor(ptdesc);
> +	tlb_remove_ptdesc(tlb, ptdesc);
> +}

Should we update p4d_free() to call the destructor, too? It looks like
it just does free_page() atm.

Will