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Message-ID: <0245d69d-8544-4068-9739-2d999c1fc599@arm.com>
Date: Tue, 24 Sep 2024 10:58:45 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
akpm@...ux-foundation.org
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>, Thomas Gleixner <tglx@...utronix.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ryan Roberts <ryan.roberts@....com>, x86@...nel.org,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Move set_pxd_safe() helpers from generic to platform
On 9/20/24 14:12, Anshuman Khandual wrote:
>
>
> On 9/20/24 12:09, David Hildenbrand wrote:
>> On 20.09.24 07:30, Anshuman Khandual wrote:
>>> set_pxd_safe() helpers that serve a specific purpose for both x86 and riscv
>>> platforms, do not need to be in the common memory code. Otherwise they just
>>> unnecessarily make the common API more complicated. This moves the helpers
>>> from common code to platform instead.
>>>
>>> Cc: Paul Walmsley <paul.walmsley@...ive.com>
>>> Cc: Palmer Dabbelt <palmer@...belt.com>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>>> Cc: David Hildenbrand <david@...hat.com>
>>> Cc: Ryan Roberts <ryan.roberts@....com>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: x86@...nel.org
>>> Cc: linux-mm@...ck.org
>>> Cc: linux-riscv@...ts.infradead.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Suggested-by: David Hildenbrand <david@...hat.com>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>>> ---
>>> arch/riscv/include/asm/pgtable.h | 19 ++++++++++++++++
>>> arch/x86/include/asm/pgtable.h | 37 +++++++++++++++++++++++++++++++
>>> include/linux/pgtable.h | 38 --------------------------------
>>> 3 files changed, 56 insertions(+), 38 deletions(-)
>>>
>>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>>> index 089f3c9f56a3..39ca652c5ebe 100644
>>> --- a/arch/riscv/include/asm/pgtable.h
>>> +++ b/arch/riscv/include/asm/pgtable.h
>>> @@ -957,6 +957,25 @@ void misc_mem_init(void);
>>> extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
>>> #define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
>>> +/*
>>> + * Use set_p*_safe(), and elide TLB flushing, when confident that *no*
>>> + * TLB flush will be required as a result of the "set". For example, use
>>> + * in scenarios where it is known ahead of time that the routine is
>>> + * setting non-present entries, or re-setting an existing entry to the
>>> + * same value. Otherwise, use the typical "set" helpers and flush the
>>> + * TLB.
>>> + */
>>> +#define set_p4d_safe(p4dp, p4d) \
>>> +({ \
>>> + WARN_ON_ONCE(p4d_present(*p4dp) && !p4d_same(*p4dp, p4d)); \
>>> + set_p4d(p4dp, p4d); \
>>> +})
>>> +
>>> +#define set_pgd_safe(pgdp, pgd) \
>>> +({ \
>>> + WARN_ON_ONCE(pgd_present(*pgdp) && !pgd_same(*pgdp, pgd)); \
>>> + set_pgd(pgdp, pgd); \
>>> +})
>>> #endif /* !__ASSEMBLY__ */
>>> #endif /* _ASM_RISCV_PGTABLE_H */
>>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>>> index e39311a89bf4..fefb52bb6b4d 100644
>>> --- a/arch/x86/include/asm/pgtable.h
>>> +++ b/arch/x86/include/asm/pgtable.h
>>> @@ -1701,6 +1701,43 @@ bool arch_is_platform_page(u64 paddr);
>>> #define arch_is_platform_page arch_is_platform_page
>>> #endif
>>> +/*
>>> + * Use set_p*_safe(), and elide TLB flushing, when confident that *no*
>>> + * TLB flush will be required as a result of the "set". For example, use
>>> + * in scenarios where it is known ahead of time that the routine is
>>> + * setting non-present entries, or re-setting an existing entry to the
>>> + * same value. Otherwise, use the typical "set" helpers and flush the
>>> + * TLB.
>>> + */
>>> +#define set_pte_safe(ptep, pte) \
>>> +({ \
>>> + WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \
>>> + set_pte(ptep, pte); \
>>> +})
>>> +
>>> +#define set_pmd_safe(pmdp, pmd) \
>>> +({ \
>>> + WARN_ON_ONCE(pmd_present(*pmdp) && !pmd_same(*pmdp, pmd)); \
>>> + set_pmd(pmdp, pmd); \
>>> +})
>>> +
>>> +#define set_pud_safe(pudp, pud) \
>>> +({ \
>>> + WARN_ON_ONCE(pud_present(*pudp) && !pud_same(*pudp, pud)); \
>>> + set_pud(pudp, pud); \
>>> +})
>>> +
>>> +#define set_p4d_safe(p4dp, p4d) \
>>> +({ \
>>> + WARN_ON_ONCE(p4d_present(*p4dp) && !p4d_same(*p4dp, p4d)); \
>>> + set_p4d(p4dp, p4d); \
>>> +})
>>> +
>>> +#define set_pgd_safe(pgdp, pgd) \
>>> +({ \
>>> + WARN_ON_ONCE(pgd_present(*pgdp) && !pgd_same(*pgdp, pgd)); \
>>> + set_pgd(pgdp, pgd); \
>>> +})
>>> #endif /* __ASSEMBLY__ */
>>
>> I'm wondering if we can completely get rid of these, for example via:
>>
>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>> index d8dbeac8b206..bc71c25930bb 100644
>> --- a/arch/x86/mm/init_64.c
>> +++ b/arch/x86/mm/init_64.c
>> @@ -79,10 +79,8 @@ DEFINE_POPULATE(pmd_populate_kernel, pmd, pte, init)
>> static inline void set_##type1##_init(type1##_t *arg1, \
>> type2##_t arg2, bool init) \
>> { \
>> - if (init) \
>> - set_##type1##_safe(arg1, arg2); \
>> - else \
>> - set_##type1(arg1, arg2); \
>> + WARN_ON_ONCE(init && ##type1##_present(*arg1) && !##type1##_same(*arg1, arg2)); \
>> + set_##type1(arg1, arg2); \
>> }
>>
>>
>> We might be able to handle the pgd_populate etc part similarly, possibly getting
>> rid of the pgd_populate_safe etc as well.
>>
>> Assuming I don't miss anything important :)
>
> Sounds feasible but will just leave that upto the x86 platform folks to
> change later on, after this patch which just moves these helpers inside
> the platform code.
>
>>
>> Ideally, we get rid of the macros here and just use inline functions ...
>>
>
> Sure, makes sense. Will change these as inline functions.
>
> -#define set_pte_safe(ptep, pte) \
> -({ \
> - WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \
> - set_pte(ptep, pte); \
> -})
> +static inline void set_pte_safe(pte_t *ptep, pte_t pte)
> +{
> + WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte));
> + set_pte(ptep, pte);
> +}
>
This has hit a road block in converting these macros as static inline
functions as suggested earlier, because pmd/pud/p4d/pgd_same() macros
are defined in generic header include/linux/pgtable.h, but way after
<asm/pgtable.h> gets included. I guess then the current patch should
be left as it is.
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