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Message-ID: <6f178f3c-40fd-45f6-a380-a218429852ca@arm.com>
Date: Fri, 20 Sep 2024 14:12:40 +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 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);
+}
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