Subject: Re: [V2, 08/10] powerpc/mm: Clear top 16 bits of va only on older cpus

From: Michael Ellerman <[email-masked]>
Date: Tue, 14 Jun 2016 14:57:25 +1000 (AEST)

On Thu, 2016-09-06 at 06:19:15 UTC, "Aneesh Kumar K.V" wrote:
> Updated patch below. MMU_FTRS_POWER4 is inherited by others, hence don't
> update that.
> 
> >From 4ed66fd24dc4f976969cc34aca8df2ddbc69fe61 Mon Sep 17 00:00:00 2001
> From: "Aneesh Kumar K.V" <[email-masked]>
> Date: Sat, 4 Jun 2016 19:58:26 +0530
> Subject: [PATCH] powerpc/mm: Clear top 16 bits of va only on older cpus
> 
> As per ISA, we need to do this only for architecture version 2.02 and
> earlier. This continued to work even for 2.07. But let's not do this for
> anything after 2.02

What are the practical effects of this?

> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> index e53ebebff474..fa314b1d667e 100644
> --- a/arch/powerpc/include/asm/mmu.h
> +++ b/arch/powerpc/include/asm/mmu.h
> @@ -24,6 +24,11 @@
>  /*
>   * This is individual features
>   */
> +/*
> + * We need to clear top 16bits of va (from the remaining 64 bits )in
> + * tlbie* instructions
> + */
> +#define MMU_FTR_TLBIE_CROP_VA		ASM_CONST(0x00008000)
>  
>  /* Enable use of high BAT registers */
>  #define MMU_FTR_USE_HIGH_BATS		ASM_CONST(0x00010000)
> @@ -124,7 +129,7 @@ enum {
>  		MMU_FTR_USE_TLBRSRV | MMU_FTR_USE_PAIRED_MAS |
>  		MMU_FTR_NO_SLBIE_B | MMU_FTR_16M_PAGE | MMU_FTR_TLBIEL |
>  		MMU_FTR_LOCKLESS_TLBIE | MMU_FTR_CI_LARGE_PAGE |
> -		MMU_FTR_1T_SEGMENT |
> +		MMU_FTR_1T_SEGMENT | MMU_FTR_TLBIE_CROP_VA |
>  #ifdef CONFIG_PPC_RADIX_MMU
>  		MMU_FTR_RADIX |
>  #endif
> diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> index eeeacf6235a3..d8a0f7ca74e1 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -137,7 +137,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
>  		.cpu_name		= "POWER4 (gp)",
>  		.cpu_features		= CPU_FTRS_POWER4,
>  		.cpu_user_features	= COMMON_USER_POWER4,
> -		.mmu_features		= MMU_FTRS_POWER4,
> +		.mmu_features		= MMU_FTRS_POWER4 | MMU_FTR_TLBIE_CROP_VA,
>  		.icache_bsize		= 128,
>  		.dcache_bsize		= 128,
>  		.num_pmcs		= 8,
> @@ -152,7 +152,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
>  		.cpu_name		= "POWER4+ (gq)",
>  		.cpu_features		= CPU_FTRS_POWER4,
>  		.cpu_user_features	= COMMON_USER_POWER4,
> -		.mmu_features		= MMU_FTRS_POWER4,
> +		.mmu_features		= MMU_FTRS_POWER4 | MMU_FTR_TLBIE_CROP_VA,
>  		.icache_bsize		= 128,
>  		.dcache_bsize		= 128,
>  		.num_pmcs		= 8,
> @@ -168,7 +168,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
>  		.cpu_features		= CPU_FTRS_PPC970,
>  		.cpu_user_features	= COMMON_USER_POWER4 |
>  			PPC_FEATURE_HAS_ALTIVEC_COMP,
> -		.mmu_features		= MMU_FTRS_PPC970,
> +		.mmu_features		= MMU_FTRS_PPC970 | MMU_FTR_TLBIE_CROP_VA,

Please add it to MMU_FTRS_PPC970, rather than at every usage.

cheers