Re: [PATCH v2 01/19] ARC: mm: use SCRATCH_DATA0 register for caching pgdir in ARCv2 only

[Mike Rapoport <rppt@kernel.org>]

On Thu, Aug 12, 2021 at 04:37:35PM -0700, Vineet Gupta wrote:
> MMU SCRATCH_DATA0 register is intended to cache task pgd. However in
> ARC700 SMP port, it has to be repurposed for reentrant interrupt
> handling, while UP port doesn't. We  currently ahandle boe usecases

					       ^ handle both

maybe ':set spell' for changelog editing? ;-)

> using a fabricated which has usual issues of dependency nesting and
> ugliness.
> 
> So clean this up: for ARC700 don't use to cache pgd (even in UP) and do
> the opposite for ARCv2.
> 
> And while here, switch to canonical pgd_offset().
> 
> Signed-off-by: Vineet Gupta <vgupta@kernel.org>
> ---
>  arch/arc/include/asm/entry-compact.h |  8 --------
>  arch/arc/include/asm/mmu.h           |  4 ----
>  arch/arc/include/asm/mmu_context.h   |  2 +-
>  arch/arc/include/asm/pgtable.h       | 23 -----------------------
>  arch/arc/mm/fault.c                  |  2 +-
>  arch/arc/mm/tlb.c                    |  4 ++--
>  arch/arc/mm/tlbex.S                  |  2 +-
>  7 files changed, 5 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/arc/include/asm/entry-compact.h b/arch/arc/include/asm/entry-compact.h
> index 6dbf5cecc8cc..5aab4f93ab8a 100644
> --- a/arch/arc/include/asm/entry-compact.h
> +++ b/arch/arc/include/asm/entry-compact.h
> @@ -126,19 +126,11 @@
>   * to be saved again on kernel mode stack, as part of pt_regs.
>   *-------------------------------------------------------------*/
>  .macro PROLOG_FREEUP_REG	reg, mem
> -#ifndef ARC_USE_SCRATCH_REG
> -	sr  \reg, [ARC_REG_SCRATCH_DATA0]
> -#else
>  	st  \reg, [\mem]
> -#endif
>  .endm
>  
>  .macro PROLOG_RESTORE_REG	reg, mem
> -#ifndef ARC_USE_SCRATCH_REG
> -	lr  \reg, [ARC_REG_SCRATCH_DATA0]
> -#else
>  	ld  \reg, [\mem]
> -#endif
>  .endm
>  
>  /*--------------------------------------------------------------
> diff --git a/arch/arc/include/asm/mmu.h b/arch/arc/include/asm/mmu.h
> index a81d1975866a..4065335a7922 100644
> --- a/arch/arc/include/asm/mmu.h
> +++ b/arch/arc/include/asm/mmu.h
> @@ -31,10 +31,6 @@
>  #define ARC_REG_SCRATCH_DATA0	0x46c
>  #endif
>  
> -#if defined(CONFIG_ISA_ARCV2) || !defined(CONFIG_SMP)
> -#define	ARC_USE_SCRATCH_REG
> -#endif
> -
>  /* Bits in MMU PID register */
>  #define __TLB_ENABLE		(1 << 31)
>  #define __PROG_ENABLE		(1 << 30)
> diff --git a/arch/arc/include/asm/mmu_context.h b/arch/arc/include/asm/mmu_context.h
> index df164066e172..49318a126879 100644
> --- a/arch/arc/include/asm/mmu_context.h
> +++ b/arch/arc/include/asm/mmu_context.h
> @@ -146,7 +146,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>  	 */
>  	cpumask_set_cpu(cpu, mm_cpumask(next));
>  
> -#ifdef ARC_USE_SCRATCH_REG
> +#ifdef CONFIG_ISA_ARCV2
>  	/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */
>  	write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
>  #endif
> diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
> index 0c3e220bd2b4..80b57c14b430 100644
> --- a/arch/arc/include/asm/pgtable.h
> +++ b/arch/arc/include/asm/pgtable.h
> @@ -284,29 +284,6 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
>  	set_pte(ptep, pteval);
>  }
>  
> -/*
> - * Macro to quickly access the PGD entry, utlising the fact that some
> - * arch may cache the pointer to Page Directory of "current" task
> - * in a MMU register
> - *
> - * Thus task->mm->pgd (3 pointer dereferences, cache misses etc simply
> - * becomes read a register
> - *
> - * ********CAUTION*******:
> - * Kernel code might be dealing with some mm_struct of NON "current"
> - * Thus use this macro only when you are certain that "current" is current
> - * e.g. when dealing with signal frame setup code etc
> - */
> -#ifdef ARC_USE_SCRATCH_REG
> -#define pgd_offset_fast(mm, addr)	\
> -({					\
> -	pgd_t *pgd_base = (pgd_t *) read_aux_reg(ARC_REG_SCRATCH_DATA0);  \
> -	pgd_base + pgd_index(addr);	\
> -})
> -#else
> -#define pgd_offset_fast(mm, addr)	pgd_offset(mm, addr)
> -#endif
> -
>  extern pgd_t swapper_pg_dir[] __aligned(PAGE_SIZE);
>  void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
>  		      pte_t *ptep);
> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
> index f5657cb68e4f..41f154320964 100644
> --- a/arch/arc/mm/fault.c
> +++ b/arch/arc/mm/fault.c
> @@ -33,7 +33,7 @@ noinline static int handle_kernel_vaddr_fault(unsigned long address)
>  	pud_t *pud, *pud_k;
>  	pmd_t *pmd, *pmd_k;
>  
> -	pgd = pgd_offset_fast(current->active_mm, address);
> +	pgd = pgd_offset(current->active_mm, address);
>  	pgd_k = pgd_offset_k(address);
>  
>  	if (!pgd_present(*pgd_k))
> diff --git a/arch/arc/mm/tlb.c b/arch/arc/mm/tlb.c
> index 8696829d37c0..349fb7a75d1d 100644
> --- a/arch/arc/mm/tlb.c
> +++ b/arch/arc/mm/tlb.c
> @@ -719,8 +719,8 @@ void arc_mmu_init(void)
>  	/* Enable the MMU */
>  	write_aux_reg(ARC_REG_PID, MMU_ENABLE);
>  
> -	/* In smp we use this reg for interrupt 1 scratch */
> -#ifdef ARC_USE_SCRATCH_REG
> +	/* In arc700/smp needed for re-entrant interrupt handling */
> +#ifdef CONFIG_ISA_ARCV2
>  	/* swapper_pg_dir is the pgd for the kernel, used by vmalloc */
>  	write_aux_reg(ARC_REG_SCRATCH_DATA0, swapper_pg_dir);
>  #endif
> diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
> index 96c3a5de9dd4..bcd2909c691f 100644
> --- a/arch/arc/mm/tlbex.S
> +++ b/arch/arc/mm/tlbex.S
> @@ -202,7 +202,7 @@ ex_saved_reg1:
>  
>  	lr  r2, [efa]
>  
> -#ifdef ARC_USE_SCRATCH_REG
> +#ifdef CONFIG_ISA_ARCV2
>  	lr  r1, [ARC_REG_SCRATCH_DATA0] ; current pgd
>  #else
>  	GET_CURR_TASK_ON_CPU  r1
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.

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