Re: [PATCH v4 05/12] mm: introduce CONFIG_ARCH_HAS_LAZY_MMU_MODE

[Ryan Roberts <ryan.roberts@arm.com>]

On 29/10/2025 10:09, Kevin Brodsky wrote:
> Architectures currently opt in for implementing lazy_mmu helpers by
> defining __HAVE_ARCH_ENTER_LAZY_MMU_MODE.
> 
> In preparation for introducing a generic lazy_mmu layer that will
> require storage in task_struct, let's switch to a cleaner approach:
> instead of defining a macro, select a CONFIG option.
> 
> This patch introduces CONFIG_ARCH_HAS_LAZY_MMU_MODE and has each
> arch select it when it implements lazy_mmu helpers.
> __HAVE_ARCH_ENTER_LAZY_MMU_MODE is removed and <linux/pgtable.h>
> relies on the new CONFIG instead.
> 
> On x86, lazy_mmu helpers are only implemented if PARAVIRT_XXL is
> selected. This creates some complications in arch/x86/boot/, because
> a few files manually undefine PARAVIRT* options. As a result
> <asm/paravirt.h> does not define the lazy_mmu helpers, but this
> breaks the build as <linux/pgtable.h> only defines them if
> !CONFIG_ARCH_HAS_LAZY_MMU_MODE. There does not seem to be a clean
> way out of this - let's just undefine that new CONFIG too.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---
>  arch/arm64/Kconfig                                 | 1 +
>  arch/arm64/include/asm/pgtable.h                   | 1 -
>  arch/powerpc/include/asm/book3s/64/tlbflush-hash.h | 2 --
>  arch/powerpc/platforms/Kconfig.cputype             | 1 +
>  arch/sparc/Kconfig                                 | 1 +
>  arch/sparc/include/asm/tlbflush_64.h               | 2 --
>  arch/x86/Kconfig                                   | 1 +
>  arch/x86/boot/compressed/misc.h                    | 1 +
>  arch/x86/boot/startup/sme.c                        | 1 +
>  arch/x86/include/asm/paravirt.h                    | 1 -
>  include/linux/pgtable.h                            | 2 +-
>  mm/Kconfig                                         | 3 +++
>  12 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6663ffd23f25..e6bf5c7311b5 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -122,6 +122,7 @@ config ARM64
>  	select ARCH_WANTS_NO_INSTR
>  	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
>  	select ARCH_HAS_UBSAN
> +	select ARCH_HAS_LAZY_MMU_MODE

nit: This list is mostly in alphabetical order. Further up the list there are a
lot of ARCH_HAS_* entries. Perhaps move it to the correct position in that lot?
Then ARCH_HAS_UBSAN stays out of order on its own.

Otherwise, all looks reasonable to me:

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

>  	select ARM_AMBA
>  	select ARM_ARCH_TIMER
>  	select ARM_GIC
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 0944e296dd4a..54f8d6bb6f22 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -80,7 +80,6 @@ static inline void queue_pte_barriers(void)
>  	}
>  }
>  
> -#define  __HAVE_ARCH_ENTER_LAZY_MMU_MODE
>  static inline void arch_enter_lazy_mmu_mode(void)
>  {
>  	/*
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> index 7704dbe8e88d..623a8a8b2d0e 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> @@ -24,8 +24,6 @@ DECLARE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
>  
>  extern void __flush_tlb_pending(struct ppc64_tlb_batch *batch);
>  
> -#define __HAVE_ARCH_ENTER_LAZY_MMU_MODE
> -
>  static inline void arch_enter_lazy_mmu_mode(void)
>  {
>  	struct ppc64_tlb_batch *batch;
> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> index 7b527d18aa5e..2942d57cf59c 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -93,6 +93,7 @@ config PPC_BOOK3S_64
>  	select IRQ_WORK
>  	select PPC_64S_HASH_MMU if !PPC_RADIX_MMU
>  	select KASAN_VMALLOC if KASAN
> +	select ARCH_HAS_LAZY_MMU_MODE
>  
>  config PPC_BOOK3E_64
>  	bool "Embedded processors"
> diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
> index a630d373e645..2bad14744ca4 100644
> --- a/arch/sparc/Kconfig
> +++ b/arch/sparc/Kconfig
> @@ -112,6 +112,7 @@ config SPARC64
>  	select NEED_PER_CPU_PAGE_FIRST_CHUNK
>  	select ARCH_SUPPORTS_SCHED_SMT if SMP
>  	select ARCH_SUPPORTS_SCHED_MC  if SMP
> +	select ARCH_HAS_LAZY_MMU_MODE
>  
>  config ARCH_PROC_KCORE_TEXT
>  	def_bool y
> diff --git a/arch/sparc/include/asm/tlbflush_64.h b/arch/sparc/include/asm/tlbflush_64.h
> index 925bb5d7a4e1..4e1036728e2f 100644
> --- a/arch/sparc/include/asm/tlbflush_64.h
> +++ b/arch/sparc/include/asm/tlbflush_64.h
> @@ -39,8 +39,6 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
>  
>  void flush_tlb_kernel_range(unsigned long start, unsigned long end);
>  
> -#define __HAVE_ARCH_ENTER_LAZY_MMU_MODE
> -
>  void flush_tlb_pending(void);
>  void arch_enter_lazy_mmu_mode(void);
>  void arch_flush_lazy_mmu_mode(void);
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index fa3b616af03a..ef4332d720ab 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -804,6 +804,7 @@ config PARAVIRT
>  config PARAVIRT_XXL
>  	bool
>  	depends on X86_64
> +	select ARCH_HAS_LAZY_MMU_MODE
>  
>  config PARAVIRT_DEBUG
>  	bool "paravirt-ops debugging"
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index db1048621ea2..cdd7f692d9ee 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -11,6 +11,7 @@
>  #undef CONFIG_PARAVIRT
>  #undef CONFIG_PARAVIRT_XXL
>  #undef CONFIG_PARAVIRT_SPINLOCKS
> +#undef CONFIG_ARCH_HAS_LAZY_MMU_MODE
>  #undef CONFIG_KASAN
>  #undef CONFIG_KASAN_GENERIC
>  
> diff --git a/arch/x86/boot/startup/sme.c b/arch/x86/boot/startup/sme.c
> index e7ea65f3f1d6..b76a7c95dfe1 100644
> --- a/arch/x86/boot/startup/sme.c
> +++ b/arch/x86/boot/startup/sme.c
> @@ -24,6 +24,7 @@
>  #undef CONFIG_PARAVIRT
>  #undef CONFIG_PARAVIRT_XXL
>  #undef CONFIG_PARAVIRT_SPINLOCKS
> +#undef CONFIG_ARCH_HAS_LAZY_MMU_MODE
>  
>  /*
>   * This code runs before CPU feature bits are set. By default, the
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index b5e59a7ba0d0..13f9cd31c8f8 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -526,7 +526,6 @@ static inline void arch_end_context_switch(struct task_struct *next)
>  	PVOP_VCALL1(cpu.end_context_switch, next);
>  }
>  
> -#define  __HAVE_ARCH_ENTER_LAZY_MMU_MODE
>  static inline void arch_enter_lazy_mmu_mode(void)
>  {
>  	PVOP_VCALL0(mmu.lazy_mode.enter);
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 32e8457ad535..9894366e768b 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -231,7 +231,7 @@ static inline int pmd_dirty(pmd_t pmd)
>   * held, but for kernel PTE updates, no lock is held). Nesting is not permitted
>   * and the mode cannot be used in interrupt context.
>   */
> -#ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
> +#ifndef CONFIG_ARCH_HAS_LAZY_MMU_MODE
>  static inline void arch_enter_lazy_mmu_mode(void) {}
>  static inline void arch_leave_lazy_mmu_mode(void) {}
>  static inline void arch_flush_lazy_mmu_mode(void) {}
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 0e26f4fc8717..5480c9a1bfb2 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1372,6 +1372,9 @@ config PT_RECLAIM
>  config FIND_NORMAL_PAGE
>  	def_bool n
>  
> +config ARCH_HAS_LAZY_MMU_MODE
> +	bool
> +
>  source "mm/damon/Kconfig"
>  
>  endmenu