linux-kernel - Re: [PATCH 1/7] mm: remove arch_flush_lazy_mmu

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Message-ID: <aLrC4reKPAz6YFn1@kernel.org>
Date: Fri, 5 Sep 2025 14:00:50 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Andreas Larsson <andreas@...sler.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Michal Hocko <mhocko@...e.com>, Nicholas Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 1/7] mm: remove arch_flush_lazy_mmu_mode()

On Thu, Sep 04, 2025 at 01:57:30PM +0100, Kevin Brodsky wrote:
> This function has only ever been used in arch/x86, so there is no
> need for other architectures to implement it. Remove it from
> linux/pgtable.h and all architectures besides x86.
> 
> The arm64 implementation is not empty but it is only called from
> arch_leave_lazy_mmu_mode(), so we can simply fold it there.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>

Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  arch/arm64/include/asm/pgtable.h                   | 9 +--------
>  arch/powerpc/include/asm/book3s/64/tlbflush-hash.h | 2 --
>  arch/sparc/include/asm/tlbflush_64.h               | 1 -
>  arch/x86/include/asm/pgtable.h                     | 3 ++-
>  include/linux/pgtable.h                            | 1 -
>  5 files changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index abd2dee416b3..728d7b6ed20a 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -101,21 +101,14 @@ static inline void arch_enter_lazy_mmu_mode(void)
>  	set_thread_flag(TIF_LAZY_MMU);
>  }
>  
> -static inline void arch_flush_lazy_mmu_mode(void)
> +static inline void arch_leave_lazy_mmu_mode(void)
>  {
>  	if (in_interrupt())
>  		return;
>  
>  	if (test_and_clear_thread_flag(TIF_LAZY_MMU_PENDING))
>  		emit_pte_barriers();
> -}
> -
> -static inline void arch_leave_lazy_mmu_mode(void)
> -{
> -	if (in_interrupt())
> -		return;
>  
> -	arch_flush_lazy_mmu_mode();
>  	clear_thread_flag(TIF_LAZY_MMU);
>  }
>  
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> index 146287d9580f..176d7fd79eeb 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
> @@ -55,8 +55,6 @@ static inline void arch_leave_lazy_mmu_mode(void)
>  	preempt_enable();
>  }
>  
> -#define arch_flush_lazy_mmu_mode()      do {} while (0)
> -
>  extern void hash__tlbiel_all(unsigned int action);
>  
>  extern void flush_hash_page(unsigned long vpn, real_pte_t pte, int psize,
> diff --git a/arch/sparc/include/asm/tlbflush_64.h b/arch/sparc/include/asm/tlbflush_64.h
> index 8b8cdaa69272..cd144eb31bdd 100644
> --- a/arch/sparc/include/asm/tlbflush_64.h
> +++ b/arch/sparc/include/asm/tlbflush_64.h
> @@ -44,7 +44,6 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end);
>  void flush_tlb_pending(void);
>  void arch_enter_lazy_mmu_mode(void);
>  void arch_leave_lazy_mmu_mode(void);
> -#define arch_flush_lazy_mmu_mode()      do {} while (0)
>  
>  /* Local cpu only.  */
>  void __flush_tlb_all(void);
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index e33df3da6980..14fd672bc9b2 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -117,7 +117,8 @@ extern pmdval_t early_pmd_flags;
>  #define pte_val(x)	native_pte_val(x)
>  #define __pte(x)	native_make_pte(x)
>  
> -#define arch_end_context_switch(prev)	do {} while(0)
> +#define arch_end_context_switch(prev)	do {} while (0)
> +#define arch_flush_lazy_mmu_mode()	do {} while (0)
>  #endif	/* CONFIG_PARAVIRT_XXL */
>  
>  static inline pmd_t pmd_set_flags(pmd_t pmd, pmdval_t set)
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 4c035637eeb7..8848e132a6be 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -234,7 +234,6 @@ static inline int pmd_dirty(pmd_t pmd)
>  #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
>  #define arch_enter_lazy_mmu_mode()	do {} while (0)
>  #define arch_leave_lazy_mmu_mode()	do {} while (0)
> -#define arch_flush_lazy_mmu_mode()	do {} while (0)
>  #endif
>  
>  #ifndef pte_batch_hint
> -- 
> 2.47.0
> 

-- 
Sincerely yours,
Mike.