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Subject: Re: [PATCH 02/10] powerpc/603: Store PGDIR physical address in a SPRG
From:   Christophe Leroy <christophe.leroy@c-s.fr>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        joakim.tjernlund@infinera.com
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <cover.1548419273.git.christophe.leroy@c-s.fr>
 <a805b78bc4c7c24ee061d1578e7ff7bb2746e54a.1548419273.git.christophe.leroy@c-s.fr>
Message-ID: <06894fe5-bc42-96b1-ecc3-7871422ef4e3@c-s.fr>
Date:   Wed, 20 Feb 2019 18:39:58 +0100
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Le 25/01/2019 à 13:34, Christophe Leroy a écrit :
> Use SPRN_SPRG5 to store the current thread PGDIR and
> avoid reading thread_struct->pgdir at every TLB miss.

I'll send out v2 with an additional patch getting rid of SPRN_SPRG_RTAS 
hence freeing SPRN_SPRG2 which I will use here instead of SPRN_SPRG5 so 
that all 6xx will benefit.

Christophe

> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>   arch/powerpc/include/asm/reg.h      |  1 +
>   arch/powerpc/kernel/cpu_setup_6xx.S |  4 ++++
>   arch/powerpc/kernel/head_32.S       | 28 ++++++++++++++++------------
>   3 files changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 1c98ef1f2d5b..ba0ab1a1431b 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -1169,6 +1169,7 @@
>   #define SPRN_SPRG_SCRATCH1	SPRN_SPRG1
>   #define SPRN_SPRG_RTAS		SPRN_SPRG2
>   #define SPRN_SPRG_603_LRU	SPRN_SPRG4
> +#define SPRN_SPRG_603_PGDIR	SPRN_SPRG5
>   #endif
>   
>   #ifdef CONFIG_40x
> diff --git a/arch/powerpc/kernel/cpu_setup_6xx.S b/arch/powerpc/kernel/cpu_setup_6xx.S
> index 8c069e96c478..4c91d1f640fe 100644
> --- a/arch/powerpc/kernel/cpu_setup_6xx.S
> +++ b/arch/powerpc/kernel/cpu_setup_6xx.S
> @@ -24,6 +24,10 @@ BEGIN_MMU_FTR_SECTION
>   	li	r10,0
>   	mtspr	SPRN_SPRG_603_LRU,r10		/* init SW LRU tracking */
>   END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
> +	lis	r10, (swapper_pg_dir - PAGE_OFFSET)@h
> +	ori	r10, r10, (swapper_pg_dir - PAGE_OFFSET)@l
> +	mtspr	SPRN_SPRG_603_PGDIR, r10
> +
>   BEGIN_FTR_SECTION
>   	bl	__init_fpu_registers
>   END_FTR_SECTION_IFCLR(CPU_FTR_FPU_UNAVAILABLE)
> diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> index c2f564690778..dbd15e03952a 100644
> --- a/arch/powerpc/kernel/head_32.S
> +++ b/arch/powerpc/kernel/head_32.S
> @@ -502,16 +502,15 @@ InstructionTLBMiss:
>   	mfspr	r3,SPRN_IMISS
>   	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
>   	cmplw	0,r1,r3
> -	mfspr	r2,SPRN_SPRG_THREAD
> +	mfspr	r2, SPRN_SPRG_603_PGDIR
>   	li	r1,_PAGE_USER|_PAGE_PRESENT|_PAGE_EXEC /* low addresses tested as user */
> -	lwz	r2,PGDIR(r2)
>   	bge-	112f
>   	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
>   	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
>   	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
>   	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
> -112:	tophys(r2,r2)
> -	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
> +	tophys(r2,r2)
> +112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
>   	lwz	r2,0(r2)		/* get pmd entry */
>   	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
>   	beq-	InstructionAddressInvalid	/* return if no mapping */
> @@ -576,16 +575,15 @@ DataLoadTLBMiss:
>   	mfspr	r3,SPRN_DMISS
>   	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
>   	cmplw	0,r1,r3
> -	mfspr	r2,SPRN_SPRG_THREAD
> +	mfspr	r2, SPRN_SPRG_603_PGDIR
>   	li	r1,_PAGE_USER|_PAGE_PRESENT /* low addresses tested as user */
> -	lwz	r2,PGDIR(r2)
>   	bge-	112f
>   	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
>   	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
>   	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
>   	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
> -112:	tophys(r2,r2)
> -	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
> +	tophys(r2,r2)
> +112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
>   	lwz	r2,0(r2)		/* get pmd entry */
>   	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
>   	beq-	DataAddressInvalid	/* return if no mapping */
> @@ -660,16 +658,15 @@ DataStoreTLBMiss:
>   	mfspr	r3,SPRN_DMISS
>   	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
>   	cmplw	0,r1,r3
> -	mfspr	r2,SPRN_SPRG_THREAD
> +	mfspr	r2, SPRN_SPRG_603_PGDIR
>   	li	r1,_PAGE_RW|_PAGE_USER|_PAGE_PRESENT /* access flags */
> -	lwz	r2,PGDIR(r2)
>   	bge-	112f
>   	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
>   	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
>   	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
>   	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
> -112:	tophys(r2,r2)
> -	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
> +	tophys(r2,r2)
> +112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
>   	lwz	r2,0(r2)		/* get pmd entry */
>   	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
>   	beq-	DataAddressInvalid	/* return if no mapping */
> @@ -1030,6 +1027,13 @@ _ENTRY(switch_mmu_context)
>   	lis	r5, abatron_pteptrs@ha
>   	stw	r4, abatron_pteptrs@l + 0x4(r5)
>   #endif
> +BEGIN_MMU_FTR_SECTION
> +#ifndef CONFIG_BDI_SWITCH
> +	lwz	r4, MM_PGD(r4)
> +#endif
> +	tophys(r4, r4)
> +	mtspr	SPRN_SPRG_603_PGDIR, r4
> +END_MMU_FTR_SECTION_IFCLR(MMU_FTR_HPTE_TABLE)
>   	li	r4,0
>   	isync
>   3:
>