Re: [PATCH 15/18] ARC: mm: support 3 levels of page tables

[Mike Rapoport]

On Tue, Aug 10, 2021 at 05:42:55PM -0700, Vineet Gupta wrote:
> ARCv2 MMU is software walked and Linux implements 2 levels of paging: pgd/pte.
> Forthcoming hw will have multiple levels, so this change preps mm code
> for same. It is also fun to try multi levels even on soft-walked code to
> ensure generic mm code is robust to handle.
> 
> overview
> ________
> 
> 2 levels {pgd, pte} : pmd is folded but pmd_* macros are valid and operate on pgd
> 3 levels {pgd, pmd, pte}:
>   - pud is folded and pud_* macros point to pgd
>   - pmd_* macros operate on actual pmd
> 
> code changes
> ____________
> 
> 1. #include <asm-generic/pgtable-nopud.h>
> 
> 2. Define CONFIG_PGTABLE_LEVELS 3
> 
> 3a. Define PMD_SHIFT, PMD_SIZE, PMD_MASK, pmd_t
> 3b. Define pmd_val() which actually deals with pmd
>     (pmd_offset(), pmd_index() are provided by generic code)
> 3c. Define pmd_alloc_one() and pmd_free() to allocate pmd
>     (pmd_populate/pmd_free already exist)
> 
> 4. Define pud_none(), pud_bad() macros based on generic pud_val() which
>    internally pertains to pgd now.
> 4b. define pud_populate() to just setup pgd
> 
> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxx>
> ---
>  arch/arc/Kconfig                      |  4 ++
>  arch/arc/include/asm/page.h           | 11 +++++
>  arch/arc/include/asm/pgalloc.h        | 22 ++++++++++
>  arch/arc/include/asm/pgtable-levels.h | 63 ++++++++++++++++++++++++---
>  arch/arc/include/asm/processor.h      |  2 +-
>  arch/arc/mm/fault.c                   |  4 ++
>  arch/arc/mm/tlb.c                     |  4 +-
>  arch/arc/mm/tlbex.S                   |  9 ++++
>  8 files changed, 111 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index 59d5b2a179f6..43cb8aaf57a2 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -314,6 +314,10 @@ config ARC_HUGEPAGE_16M
>  
>  endchoice
>  
> +config PGTABLE_LEVELS
> +	int "Number of Page table levels"
> +	default 2
> +
>  config ARC_COMPACT_IRQ_LEVELS
>  	depends on ISA_ARCOMPACT
>  	bool "Setup Timer IRQ as high Priority"
> diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
> index 313e6f543d2d..df3cc154ae4a 100644
> --- a/arch/arc/include/asm/page.h
> +++ b/arch/arc/include/asm/page.h
> @@ -41,6 +41,17 @@ typedef struct {
>  #define pgd_val(x)	((x).pgd)
>  #define __pgd(x)	((pgd_t) { (x) })
>  
> +#if CONFIG_PGTABLE_LEVELS > 2
> +
> +typedef struct {
> +	unsigned long pmd;
> +} pmd_t;
> +
> +#define pmd_val(x)	((x).pmd)
> +#define __pmd(x)	((pmd_t) { (x) })
> +
> +#endif
> +
>  typedef struct {
>  #ifdef CONFIG_ARC_HAS_PAE40
>  	unsigned long long pte;
> diff --git a/arch/arc/include/asm/pgalloc.h b/arch/arc/include/asm/pgalloc.h
> index 0cf73431eb89..01c2d84418ed 100644
> --- a/arch/arc/include/asm/pgalloc.h
> +++ b/arch/arc/include/asm/pgalloc.h
> @@ -86,6 +86,28 @@ static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
>  }
>  
>  
> +#if CONFIG_PGTABLE_LEVELS > 2
> +
> +static inline void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
> +{
> +	set_pud(pudp, __pud((unsigned long)pmdp));
> +}
> +
> +static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr)
> +{
> +	return (pmd_t *)__get_free_page(
> +		GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_ZERO);
> +}
> +
> +static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd)
> +{
> +	free_page((unsigned long)pmd);
> +}
> +
> +#define __pmd_free_tlb(tlb, pmd, addr)  pmd_free((tlb)->mm, pmd)
> +
> +#endif
> +
>  /*
>   * With software-only page-tables, addr-split for traversal is tweakable and
>   * that directly governs how big tables would be at each level.
> diff --git a/arch/arc/include/asm/pgtable-levels.h b/arch/arc/include/asm/pgtable-levels.h
> index 8ece75335bb5..1c2f022d4ad0 100644
> --- a/arch/arc/include/asm/pgtable-levels.h
> +++ b/arch/arc/include/asm/pgtable-levels.h
> @@ -10,6 +10,8 @@
>  #ifndef _ASM_ARC_PGTABLE_LEVELS_H
>  #define _ASM_ARC_PGTABLE_LEVELS_H
>  
> +#if CONFIG_PGTABLE_LEVELS == 2
> +
>  /*
>   * 2 level paging setup for software walked MMUv3 (ARC700) and MMUv4 (HS)
>   *
> @@ -37,16 +39,38 @@
>  #define PGDIR_SHIFT		21
>  #endif
>  
> -#define PGDIR_SIZE		BIT(PGDIR_SHIFT)	/* vaddr span, not PDG sz */
> -#define PGDIR_MASK		(~(PGDIR_SIZE - 1))
> +#else
> +
> +/*
> + * A default 3 level paging testing setup in software walked MMU
> + *   MMUv4 (8K page): <4> : <7> : <8> : <13>
> + */
> +#define PGDIR_SHIFT		28
> +#if CONFIG_PGTABLE_LEVELS > 2
> +#define PMD_SHIFT		21
> +#endif
> +
> +#endif
>  
> +#define PGDIR_SIZE		BIT(PGDIR_SHIFT)
> +#define PGDIR_MASK		(~(PGDIR_SIZE - 1))
>  #define PTRS_PER_PGD		BIT(32 - PGDIR_SHIFT)
>  
> -#define PTRS_PER_PTE		BIT(PGDIR_SHIFT - PAGE_SHIFT)
> +#if CONFIG_PGTABLE_LEVELS > 2
> +#define PMD_SIZE		BIT(PMD_SHIFT)
> +#define PMD_MASK		(~(PMD_SIZE - 1))
> +#define PTRS_PER_PMD		BIT(PGDIR_SHIFT - PMD_SHIFT)

Maybe move these into the previous #if CONFIG_PGTABLE_LEVELS > 2?

> +#endif
> +
> +#define PTRS_PER_PTE		BIT(PMD_SHIFT - PAGE_SHIFT)
>  
>  #ifndef __ASSEMBLY__
>  
> +#if CONFIG_PGTABLE_LEVELS > 2
> +#include <asm-generic/pgtable-nopud.h>
> +#else
>  #include <asm-generic/pgtable-nopmd.h>
> +#endif
>  
>  /*
>   * 1st level paging: pgd
> @@ -57,9 +81,35 @@
>  #define pgd_ERROR(e) \
>  	pr_crit("%s:%d: bad pgd %08lx.\n", __FILE__, __LINE__, pgd_val(e))
>  
> +#if CONFIG_PGTABLE_LEVELS > 2
> +
> +/* In 3 level paging, pud_* macros work on pgd */
> +#define pud_none(x)		(!pud_val(x))
> +#define pud_bad(x)		((pud_val(x) & ~PAGE_MASK))
> +#define pud_present(x)		(pud_val(x))
> +#define pud_clear(xp)		do { pud_val(*(xp)) = 0; } while (0)
> +#define pud_pgtable(pud)	((pmd_t *)(pud_val(pud) & PAGE_MASK))
> +#define pud_page(pud)		virt_to_page(pud_pgtable(pud))
> +#define set_pud(pudp, pud)	(*(pudp) = pud)
> +
> +/*
> + * 2nd level paging: pmd
> + */
> +#define pmd_ERROR(e) \
> +	pr_crit("%s:%d: bad pmd %08lx.\n", __FILE__, __LINE__, pmd_val(e))
> +
> +#define pmd_pfn(pmd)		((pmd_val(pmd) & PMD_MASK) >> PAGE_SHIFT)
> +#define pfn_pmd(pfn,prot)	__pmd(((pfn) << PAGE_SHIFT) | pgprot_val(prot))
> +#define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
> +
> +#endif
> +
>  /*
> - * Due to the strange way generic pgtable level folding works, in a 2 level
> - * setup, pmd_val() returns pgd, so these pmd_* macros actually work on pgd
> + * Due to the strange way generic pgtable level folding works, the pmd_* macros
> + *  - are valid even for 2 levels (which supposedly only has pgd - pte)
> + *  - behave differently for 2 vs. 3
> + * In 2  level paging        (pgd -> pte), pmd_* macros work on pgd
> + * In 3+ level paging (pgd -> pmd -> pte), pmd_* macros work on pmd
>   */
>  #define pmd_none(x)		(!pmd_val(x))
>  #define pmd_bad(x)		((pmd_val(x) & ~PAGE_MASK))
> @@ -70,6 +120,9 @@
>  #define set_pmd(pmdp, pmd)	(*(pmdp) = pmd)
>  #define pmd_pgtable(pmd)	((pgtable_t) pmd_page_vaddr(pmd))
>  
> +/*
> + * 3rd level paging: pte
> + */
>  #define pte_ERROR(e) \
>  	pr_crit("%s:%d: bad pte %08lx.\n", __FILE__, __LINE__, pte_val(e))
>  
> diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
> index e4031ecd3c8c..f28afcf5c6d1 100644
> --- a/arch/arc/include/asm/processor.h
> +++ b/arch/arc/include/asm/processor.h
> @@ -93,7 +93,7 @@ extern unsigned int get_wchan(struct task_struct *p);
>  #define VMALLOC_START	(PAGE_OFFSET - (CONFIG_ARC_KVADDR_SIZE << 20))
>  
>  /* 1 PGDIR_SIZE each for fixmap/pkmap, 2 PGDIR_SIZE gutter (see asm/highmem.h) */
> -#define VMALLOC_SIZE	((CONFIG_ARC_KVADDR_SIZE << 20) - PGDIR_SIZE * 4)
> +#define VMALLOC_SIZE	((CONFIG_ARC_KVADDR_SIZE << 20) - PMD_SIZE * 4)
>  
>  #define VMALLOC_END	(VMALLOC_START + VMALLOC_SIZE)
>  
> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
> index 41f154320964..8da2f0ad8c69 100644
> --- a/arch/arc/mm/fault.c
> +++ b/arch/arc/mm/fault.c
> @@ -39,6 +39,8 @@ noinline static int handle_kernel_vaddr_fault(unsigned long address)
>  	if (!pgd_present(*pgd_k))
>  		goto bad_area;
>  
> +	set_pgd(pgd, *pgd_k);
> +
>  	p4d = p4d_offset(pgd, address);
>  	p4d_k = p4d_offset(pgd_k, address);
>  	if (!p4d_present(*p4d_k))
> @@ -49,6 +51,8 @@ noinline static int handle_kernel_vaddr_fault(unsigned long address)
>  	if (!pud_present(*pud_k))
>  		goto bad_area;
>  
> +	set_pud(pud, *pud_k);
> +
>  	pmd = pmd_offset(pud, address);
>  	pmd_k = pmd_offset(pud_k, address);
>  	if (!pmd_present(*pmd_k))
> diff --git a/arch/arc/mm/tlb.c b/arch/arc/mm/tlb.c
> index 34f16e0b41e6..77da83569b36 100644
> --- a/arch/arc/mm/tlb.c
> +++ b/arch/arc/mm/tlb.c
> @@ -658,8 +658,8 @@ char *arc_mmu_mumbojumbo(int cpu_id, char *buf, int len)
>  			  IS_USED_CFG(CONFIG_TRANSPARENT_HUGEPAGE));
>  
>  	n += scnprintf(buf + n, len - n,
> -		      "MMU [v%x]\t: %dk PAGE, %sJTLB %d (%dx%d), uDTLB %d, uITLB %d%s%s\n",
> -		       p_mmu->ver, p_mmu->pg_sz_k, super_pg,
> +		      "MMU [v%x]\t: %dk PAGE, %s, swalk %d lvl, JTLB %d (%dx%d), uDTLB %d, uITLB %d%s%s\n",
> +		       p_mmu->ver, p_mmu->pg_sz_k, super_pg,  CONFIG_PGTABLE_LEVELS,
>  		       p_mmu->sets * p_mmu->ways, p_mmu->sets, p_mmu->ways,
>  		       p_mmu->u_dtlb, p_mmu->u_itlb,
>  		       IS_AVAIL2(p_mmu->pae, ", PAE40 ", CONFIG_ARC_HAS_PAE40));
> diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
> index d08bd09a0afc..5f6bfdfda1be 100644
> --- a/arch/arc/mm/tlbex.S
> +++ b/arch/arc/mm/tlbex.S
> @@ -173,6 +173,15 @@ ex_saved_reg1:
>  	tst	r3, r3
>  	bz	do_slow_path_pf         ; if no Page Table, do page fault
>  
> +#if CONFIG_PGTABLE_LEVELS > 2
> +	lsr     r0, r2, PMD_SHIFT	; Bits for indexing into PMD
> +	and	r0, r0, (PTRS_PER_PMD - 1)
> +	ld.as	r1, [r3, r0]		; PMD entry
> +	tst	r1, r1
> +	bz	do_slow_path_pf
> +	mov	r3, r1
> +#endif
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  	and.f	0, r3, _PAGE_HW_SZ	; Is this Huge PMD (thp)
>  	add2.nz	r1, r1, r0
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.