Re: [PATCH v6 06/14] mm: introduce CONFIG_ARCH_HAS_LAZY_MMU_MODE

Andreas Larsson
2026-01-14T07:27:52Z

On 2025-12-15 16:03, 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.
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> 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 | 7 +++++++
> 12 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 93173f0a09c7..3fb4603c0e16 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -35,6 +35,7 @@ config ARM64
> select ARCH_HAS_KCOV
> select ARCH_HAS_KERNEL_FPU_SUPPORT if KERNEL_MODE_NEON
> select ARCH_HAS_KEEPINITRD
> + select ARCH_HAS_LAZY_MMU_MODE
> select ARCH_HAS_MEMBARRIER_SYNC_CORE
> select ARCH_HAS_MEM_ENCRYPT
> select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 64d5f1d9cce9..f7d66c261347 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 2d45f57df169..565c1b7c3eae 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 4c321a8ea896..f399917c17bd 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 80527299f859..2427a66cb0fe 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -808,6 +808,7 @@ 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 fd855e32c9b9..4f86c5903e03 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 1abc4a1c3d72..d46d86959bd6 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -235,7 +235,7 @@ static inline int pmd_dirty(pmd_t pmd)
> *
> * 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 bd0ea5454af8..62073bd61544 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1464,6 +1464,13 @@ config PT_RECLAIM
> config FIND_NORMAL_PAGE
> def_bool n
>
> +config ARCH_HAS_LAZY_MMU_MODE
> + bool
> + help
> + The architecture uses the lazy MMU mode. This allows changes to
> + MMU-related architectural state to be deferred until the mode is
> + exited. See <linux/pgtable.h> for details.
> +
> source "mm/damon/Kconfig"
>
> endmenu

Acked-by: Andreas Larsson <andreas@gaisler.com> # sparc

Cheers,
Andreas