Subject: Re: [PATCH v3 4/5] powerpc/mm: Allow up to 64 low slices

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 29 Jan 2018 11:59:10 +0530

Christophe Leroy <[email-masked]> writes:

> While the implementation of the "slices" address space allows
> a significant amount of high slices, it limits the number of
> low slices to 16 due to the use of a single u64 low_slices_psize
> element in struct mm_context_t
>
> On the 8xx, the minimum slice size is the size of the area
> covered by a single PMD entry, ie 4M in 4K pages mode and 64M in
> 16K pages mode. This means we could have at least 64 slices.
>
> In order to override this limitation, this patch switches the
> handling of low_slices_psize to char array as done already for
> high_slices_psize. This allows to increase the number of low
> slices to 64 on the 8xx.
>

Maybe update the subject to "make low slice also a bitmap".Also indicate
that the bitmap functions optimize the operation if the bitmapsize les
<= long ?

Also switch the 8xx to higher value in the another patch?

> Signed-off-by: Christophe Leroy <[email-masked]>
> ---
>  v2: Usign slice_bitmap_xxx() macros instead of bitmap_xxx() functions.
>  v3: keep low_slices as a u64, this allows 64 slices which is enough.
>  
>  arch/powerpc/include/asm/book3s/64/mmu.h |  3 +-
>  arch/powerpc/include/asm/mmu-8xx.h       |  7 +++-
>  arch/powerpc/include/asm/paca.h          |  2 +-
>  arch/powerpc/include/asm/slice.h         |  1 -
>  arch/powerpc/include/asm/slice_32.h      |  2 ++
>  arch/powerpc/include/asm/slice_64.h      |  2 ++
>  arch/powerpc/kernel/paca.c               |  3 +-
>  arch/powerpc/mm/hash_utils_64.c          | 13 ++++----
>  arch/powerpc/mm/slb_low.S                |  8 +++--
>  arch/powerpc/mm/slice.c                  | 57 +++++++++++++++++---------------
>  10 files changed, 56 insertions(+), 42 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> index c9448e19847a..b076a2d74c69 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -91,7 +91,8 @@ typedef struct {
>  	struct npu_context *npu_context;
>  
>  #ifdef CONFIG_PPC_MM_SLICES
> -	u64 low_slices_psize;	/* SLB page size encodings */
> +	 /* SLB page size encodings*/
> +	unsigned char low_slices_psize[BITS_PER_LONG / BITS_PER_BYTE];
>  	unsigned char high_slices_psize[SLICE_ARRAY_SIZE];
>  	unsigned long slb_addr_limit;
>  #else
> diff --git a/arch/powerpc/include/asm/mmu-8xx.h b/arch/powerpc/include/asm/mmu-8xx.h
> index 5f89b6010453..5f37ba06b56c 100644
> --- a/arch/powerpc/include/asm/mmu-8xx.h
> +++ b/arch/powerpc/include/asm/mmu-8xx.h
> @@ -164,6 +164,11 @@
>   */
>  #define SPRN_M_TW	799
>  
> +#ifdef CONFIG_PPC_MM_SLICES
> +#include <asm/slice_32.h>
> +#define SLICE_ARRAY_SIZE	(1 << (32 - SLICE_LOW_SHIFT - 1))
> +#endif
> +
>  #ifndef __ASSEMBLY__
>  typedef struct {
>  	unsigned int id;
> @@ -171,7 +176,7 @@ typedef struct {
>  	unsigned long vdso_base;
>  #ifdef CONFIG_PPC_MM_SLICES
>  	u16 user_psize;		/* page size index */
> -	u64 low_slices_psize;	/* page size encodings */
> +	unsigned char low_slices_psize[SLICE_ARRAY_SIZE];
>  	unsigned char high_slices_psize[0];
>  	unsigned long slb_addr_limit;
>  #endif
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index 23ac7fc0af23..a3e531fe9ac7 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -141,7 +141,7 @@ struct paca_struct {
>  #ifdef CONFIG_PPC_BOOK3S
>  	mm_context_id_t mm_ctx_id;
>  #ifdef CONFIG_PPC_MM_SLICES
> -	u64 mm_ctx_low_slices_psize;
> +	unsigned char mm_ctx_low_slices_psize[BITS_PER_LONG / BITS_PER_BYTE];
>  	unsigned char mm_ctx_high_slices_psize[SLICE_ARRAY_SIZE];
>  	unsigned long mm_ctx_slb_addr_limit;
>  #else
> diff --git a/arch/powerpc/include/asm/slice.h b/arch/powerpc/include/asm/slice.h
> index 2b4b70de7e71..b67ba8faa507 100644
> --- a/arch/powerpc/include/asm/slice.h
> +++ b/arch/powerpc/include/asm/slice.h
> @@ -16,7 +16,6 @@
>  #define HAVE_ARCH_UNMAPPED_AREA
>  #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
>  
> -#define SLICE_LOW_SHIFT		28
>  #define SLICE_LOW_TOP		(0x100000000ull)
>  #define SLICE_NUM_LOW		(SLICE_LOW_TOP >> SLICE_LOW_SHIFT)
>  #define GET_LOW_SLICE_INDEX(addr)	((addr) >> SLICE_LOW_SHIFT)
> diff --git a/arch/powerpc/include/asm/slice_32.h b/arch/powerpc/include/asm/slice_32.h
> index 7e27c0dfb913..349187c20100 100644
> --- a/arch/powerpc/include/asm/slice_32.h
> +++ b/arch/powerpc/include/asm/slice_32.h
> @@ -2,6 +2,8 @@
>  #ifndef _ASM_POWERPC_SLICE_32_H
>  #define _ASM_POWERPC_SLICE_32_H
>  
> +#define SLICE_LOW_SHIFT		26	/* 64 slices */
> +
>  #define SLICE_HIGH_SHIFT	0
>  #define SLICE_NUM_HIGH		0ul
>  #define GET_HIGH_SLICE_INDEX(addr)	(addr & 0)
> diff --git a/arch/powerpc/include/asm/slice_64.h b/arch/powerpc/include/asm/slice_64.h
> index 9d1c97b83010..0959475239c6 100644
> --- a/arch/powerpc/include/asm/slice_64.h
> +++ b/arch/powerpc/include/asm/slice_64.h
> @@ -2,6 +2,8 @@
>  #ifndef _ASM_POWERPC_SLICE_64_H
>  #define _ASM_POWERPC_SLICE_64_H
>  
> +#define SLICE_LOW_SHIFT		28
> +

You are moving the LOW_SHIFT here, may be you can fix that up in earlier
patch as reviewed there.

>  #define SLICE_HIGH_SHIFT	40
>  #define SLICE_NUM_HIGH		(H_PGTABLE_RANGE >> SLICE_HIGH_SHIFT)
>  #define GET_HIGH_SLICE_INDEX(addr)	((addr) >> SLICE_HIGH_SHIFT)
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index d6597038931d..8e1566bf82b8 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -264,7 +264,8 @@ void copy_mm_to_paca(struct mm_struct *mm)
>  #ifdef CONFIG_PPC_MM_SLICES
>  	VM_BUG_ON(!mm->context.slb_addr_limit);
>  	get_paca()->mm_ctx_slb_addr_limit = mm->context.slb_addr_limit;
> -	get_paca()->mm_ctx_low_slices_psize = context->low_slices_psize;
> +	memcpy(&get_paca()->mm_ctx_low_slices_psize,
> +	       &context->low_slices_psize, sizeof(context->low_slices_psize));
>  	memcpy(&get_paca()->mm_ctx_high_slices_psize,
>  	       &context->high_slices_psize, TASK_SLICE_ARRAY_SZ(mm));
>  #else /* CONFIG_PPC_MM_SLICES */
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 655a5a9a183d..da696565b969 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -1097,19 +1097,18 @@ unsigned int hash_page_do_lazy_icache(unsigned int pp, pte_t pte, int trap)
>  #ifdef CONFIG_PPC_MM_SLICES
>  static unsigned int get_paca_psize(unsigned long addr)
>  {
> -	u64 lpsizes;
> -	unsigned char *hpsizes;
> +	unsigned char *psizes;
>  	unsigned long index, mask_index;
>  
>  	if (addr < SLICE_LOW_TOP) {
> -		lpsizes = get_paca()->mm_ctx_low_slices_psize;
> +		psizes = get_paca()->mm_ctx_low_slices_psize;
>  		index = GET_LOW_SLICE_INDEX(addr);
> -		return (lpsizes >> (index * 4)) & 0xF;
> +	} else {
> +		psizes = get_paca()->mm_ctx_high_slices_psize;
> +		index = GET_HIGH_SLICE_INDEX(addr);
>  	}
> -	hpsizes = get_paca()->mm_ctx_high_slices_psize;
> -	index = GET_HIGH_SLICE_INDEX(addr);
>  	mask_index = index & 0x1;
> -	return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xF;
> +	return (psizes[index >> 1] >> (mask_index * 4)) & 0xF;
>  }
>  
>  #else
> diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
> index 2cf5ef3fc50d..2c7c717fd2ea 100644
> --- a/arch/powerpc/mm/slb_low.S
> +++ b/arch/powerpc/mm/slb_low.S
> @@ -200,10 +200,12 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
>  5:
>  	/*
>  	 * Handle lpsizes
> -	 * r9 is get_paca()->context.low_slices_psize, r11 is index
> +	 * r9 is get_paca()->context.low_slices_psize[index], r11 is mask_index
>  	 */
> -	ld	r9,PACALOWSLICESPSIZE(r13)
> -	mr	r11,r10
> +	srdi    r11,r10,1 /* index */
> +	addi	r9,r11,PACALOWSLICESPSIZE
> +	lbzx	r9,r13,r9		/* r9 is lpsizes[r11] */
> +	rldicl	r11,r10,0,63		/* r11 = r10 & 0x1 */
>  6:
>  	sldi	r11,r11,2  /* index * 4 */
>  	/* Extract the psize and multiply to get an array offset */
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 549704dfa777..3d573a038d42 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -148,18 +148,20 @@ static void slice_mask_for_free(struct mm_struct *mm, struct slice_mask *ret,
>  static void slice_mask_for_size(struct mm_struct *mm, int psize, struct slice_mask *ret,
>  				unsigned long high_limit)
>  {
> -	unsigned char *hpsizes;
> +	unsigned char *hpsizes, *lpsizes;
>  	int index, mask_index;
>  	unsigned long i;
> -	u64 lpsizes;
>  
>  	ret->low_slices = 0;
>  	slice_bitmap_zero(ret->high_slices, SLICE_NUM_HIGH);
>  
>  	lpsizes = mm->context.low_slices_psize;
> -	for (i = 0; i < SLICE_NUM_LOW; i++)
> -		if (((lpsizes >> (i * 4)) & 0xf) == psize)
> +	for (i = 0; i < SLICE_NUM_LOW; i++) {
> +		mask_index = i & 0x1;
> +		index = i >> 1;
> +		if (((lpsizes[index] >> (mask_index * 4)) & 0xf) == psize)
>  			ret->low_slices |= 1u << i;
> +	}
>  
>  	if (high_limit <= SLICE_LOW_TOP)
>  		return;
> @@ -211,8 +213,7 @@ static void slice_convert(struct mm_struct *mm, struct slice_mask mask, int psiz
>  {
>  	int index, mask_index;
>  	/* Write the new slice psize bits */
> -	unsigned char *hpsizes;
> -	u64 lpsizes;
> +	unsigned char *hpsizes, *lpsizes;
>  	unsigned long i, flags;
>  
>  	slice_dbg("slice_convert(mm=%p, psize=%d)\n", mm, psize);
> @@ -225,12 +226,13 @@ static void slice_convert(struct mm_struct *mm, struct slice_mask mask, int psiz
>  
>  	lpsizes = mm->context.low_slices_psize;
>  	for (i = 0; i < SLICE_NUM_LOW; i++)
> -		if (mask.low_slices & (1u << i))
> -			lpsizes = (lpsizes & ~(0xful << (i * 4))) |
> -				(((unsigned long)psize) << (i * 4));
> -
> -	/* Assign the value back */
> -	mm->context.low_slices_psize = lpsizes;
> +		if (mask.low_slices & (1u << i)) {
> +			mask_index = i & 0x1;
> +			index = i >> 1;
> +			lpsizes[index] = (lpsizes[index] &
> +					  ~(0xf << (mask_index * 4))) |
> +				(((unsigned long)psize) << (mask_index * 4));
> +		}
>  
>  	hpsizes = mm->context.high_slices_psize;
>  	for (i = 0; i < GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit); i++) {
> @@ -629,7 +631,7 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp,
>  
>  unsigned int get_slice_psize(struct mm_struct *mm, unsigned long addr)
>  {
> -	unsigned char *hpsizes;
> +	unsigned char *psizes;
>  	int index, mask_index;
>  
>  	/*
> @@ -643,15 +645,14 @@ unsigned int get_slice_psize(struct mm_struct *mm, unsigned long addr)
>  #endif
>  	}
>  	if (addr < SLICE_LOW_TOP) {
> -		u64 lpsizes;
> -		lpsizes = mm->context.low_slices_psize;
> +		psizes = mm->context.low_slices_psize;
>  		index = GET_LOW_SLICE_INDEX(addr);
> -		return (lpsizes >> (index * 4)) & 0xf;
> +	} else {
> +		psizes = mm->context.high_slices_psize;
> +		index = GET_HIGH_SLICE_INDEX(addr);
>  	}
> -	hpsizes = mm->context.high_slices_psize;
> -	index = GET_HIGH_SLICE_INDEX(addr);
>  	mask_index = index & 0x1;
> -	return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xf;
> +	return (psizes[index >> 1] >> (mask_index * 4)) & 0xf;
>  }
>  EXPORT_SYMBOL_GPL(get_slice_psize);
>  
> @@ -672,8 +673,8 @@ EXPORT_SYMBOL_GPL(get_slice_psize);
>  void slice_set_user_psize(struct mm_struct *mm, unsigned int psize)
>  {
>  	int index, mask_index;
> -	unsigned char *hpsizes;
> -	unsigned long flags, lpsizes;
> +	unsigned char *hpsizes, *lpsizes;
> +	unsigned long flags;
>  	unsigned int old_psize;
>  	int i;
>  
> @@ -691,12 +692,14 @@ void slice_set_user_psize(struct mm_struct *mm, unsigned int psize)
>  	wmb();
>  
>  	lpsizes = mm->context.low_slices_psize;
> -	for (i = 0; i < SLICE_NUM_LOW; i++)
> -		if (((lpsizes >> (i * 4)) & 0xf) == old_psize)
> -			lpsizes = (lpsizes & ~(0xful << (i * 4))) |
> -				(((unsigned long)psize) << (i * 4));
> -	/* Assign the value back */
> -	mm->context.low_slices_psize = lpsizes;
> +	for (i = 0; i < SLICE_NUM_LOW; i++) {
> +		mask_index = i & 0x1;
> +		index = i >> 1;
> +		if (((lpsizes[index] >> (mask_index * 4)) & 0xf) == old_psize)
> +			lpsizes[index] = (lpsizes[index] &
> +					  ~(0xf << (mask_index * 4))) |
> +				(((unsigned long)psize) << (mask_index * 4));
> +	}
>  
>  	hpsizes = mm->context.high_slices_psize;
>  	for (i = 0; i < SLICE_NUM_HIGH; i++) {
> -- 
> 2.13.3