linux-kernel - Re: [PATCH 05/10] riscv: mm: Skip pgtable level check in {pud,p4d}_alloc

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Message-ID: <2aed338a-97a4-40e3-8a95-99458756ca28@ghiti.fr>
Date: Fri, 3 Jan 2025 11:31:19 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Linus Walleij <linus.walleij@...aro.org>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, "Mike Rapoport (IBM)"
 <rppt@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>,
 Matthew Wilcox <willy@...radead.org>, linux-alpha@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
 linux-mips@...r.kernel.org, linux-openrisc@...r.kernel.org,
 linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
 linux-um@...ts.infradead.org, loongarch@...ts.linux.dev, x86@...nel.org
Subject: Re: [PATCH 05/10] riscv: mm: Skip pgtable level check in
 {pud,p4d}_alloc_one

Hi Kevin,

On 19/12/2024 17:44, Kevin Brodsky wrote:
> {pmd,pud,p4d}_alloc_one() is never called if the corresponding page
> table level is folded, as {pmd,pud,p4d}_alloc() already does the
> required check. We can therefore remove the runtime page table level
> checks in {pud,p4d}_alloc_one. The PUD helper becomes equivalent to
> the generic version, so we remove it altogether.
>
> This is consistent with the way arm64 and x86 handle this situation
> (runtime check in p4d_free() only).
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> ---
>   arch/riscv/include/asm/pgalloc.h | 22 ++++------------------
>   1 file changed, 4 insertions(+), 18 deletions(-)
>
> diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> index f52264304f77..8ad0bbe838a2 100644
> --- a/arch/riscv/include/asm/pgalloc.h
> +++ b/arch/riscv/include/asm/pgalloc.h
> @@ -12,7 +12,6 @@
>   #include <asm/tlb.h>
>   
>   #ifdef CONFIG_MMU
> -#define __HAVE_ARCH_PUD_ALLOC_ONE
>   #define __HAVE_ARCH_PUD_FREE
>   #include <asm-generic/pgalloc.h>
>   
> @@ -88,15 +87,6 @@ static inline void pgd_populate_safe(struct mm_struct *mm, pgd_t *pgd,
>   	}
>   }
>   
> -#define pud_alloc_one pud_alloc_one
> -static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
> -{
> -	if (pgtable_l4_enabled)
> -		return __pud_alloc_one(mm, addr);
> -
> -	return NULL;
> -}
> -
>   #define pud_free pud_free
>   static inline void pud_free(struct mm_struct *mm, pud_t *pud)
>   {
> @@ -118,15 +108,11 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
>   #define p4d_alloc_one p4d_alloc_one
>   static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
>   {
> -	if (pgtable_l5_enabled) {
> -		gfp_t gfp = GFP_PGTABLE_USER;
> -
> -		if (mm == &init_mm)
> -			gfp = GFP_PGTABLE_KERNEL;
> -		return (p4d_t *)get_zeroed_page(gfp);
> -	}
> +	gfp_t gfp = GFP_PGTABLE_USER;
>   
> -	return NULL;
> +	if (mm == &init_mm)
> +		gfp = GFP_PGTABLE_KERNEL;
> +	return (p4d_t *)get_zeroed_page(gfp);
>   }
>   
>   static inline void __p4d_free(struct mm_struct *mm, p4d_t *p4d)


Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex