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Subject: Re: [PATCH v3 4/5] powerpc/mm: Allow up to 64 low slices
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Scott Wood <oss@buserror.net>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <6920f6efe2dcdabf59350b2d31ee6bd4bdef57f4.1516783089.git.christophe.leroy@c-s.fr>
 <5dfafb3f0e2438e43f44917ffcf70e3daa4f37ee.1516783089.git.christophe.leroy@c-s.fr>
 <87po5t18ll.fsf@linux.vnet.ibm.com>
From:   Christophe LEROY <christophe.leroy@c-s.fr>
Message-ID: <2e59ae26-ba19-5416-b8b3-d51517c280b4@c-s.fr>
Date:   Sat, 10 Feb 2018 13:58:04 +0100
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Le 29/01/2018 à 07:29, Aneesh Kumar K.V a écrit :
> Christophe Leroy <christophe.leroy@c-s.fr> 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 ?

As explained below above the ---, this new version don't do that 
anymore, as 64 slices is enough.

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

Ok

Christophe

> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>>   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.

Yes, done in earlier patch now.

> 
>>   #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