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

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Message-ID: <39925677-4619-411d-b0b1-40f9db09374f@arm.com>
Date: Fri, 3 Jan 2025 11:36:03 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Alexandre Ghiti <alex@...ti.fr>, 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,
 Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH 05/10] riscv: mm: Skip pgtable level check in
 {pud,p4d}_alloc_one

+Qi

On 03/01/2025 11:31, Alexandre Ghiti wrote:
> 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 for the review! Just FYI this patch is now part of Qi's series
[1], I will drop it when posting the next version of this series.

- Kevin

[1]
https://lore.kernel.org/linux-mm/84ddf857508b98a195a790bc6ff6ab8849b44633.1735549103.git.zhengqi.arch@bytedance.com/