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Message-ID: <YRjd5N012YInbZqX@kernel.org>
Date: Sun, 15 Aug 2021 12:27:00 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Vineet Gupta <vgupta@...nel.org>
Cc: linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v2 01/19] ARC: mm: use SCRATCH_DATA0 register for caching
pgdir in ARCv2 only
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@...nel.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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