[PATCH 2/2] powerpc/64s: Disallow PROT_SAO in LPARs by default

[Nicholas Piggin]

Excerpts from Shawn Anastasio's message of August 21, 2020 11:08 am:
> Since migration of guests using SAO to ISA 3.1 hosts may cause issues,
> disable PROT_SAO in LPARs by default and introduce a new Kconfig option
> PPC_PROT_SAO_LPAR to allow users to enable it if desired.

I think this should be okay. Could you also update the selftest to skip
if we have PPC_FEATURE2_ARCH_3_1 set?

Thanks,
Nick

Acked-by: Nicholas Piggin <npiggin at gmail.com>

> 
> Signed-off-by: Shawn Anastasio <shawn at anastas.io>
> ---
>  arch/powerpc/Kconfig            | 12 ++++++++++++
>  arch/powerpc/include/asm/mman.h |  9 +++++++--
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1f48bbfb3ce9..65bed1fdeaad 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -860,6 +860,18 @@ config PPC_SUBPAGE_PROT
>  
>  	  If unsure, say N here.
>  
> +config PPC_PROT_SAO_LPAR
> +	bool "Support PROT_SAO mappings in LPARs"
> +	depends on PPC_BOOK3S_64
> +	help
> +	  This option adds support for PROT_SAO mappings from userspace
> +	  inside LPARs on supported CPUs.
> +
> +	  This may cause issues when performing guest migration from
> +	  a CPU that supports SAO to one that does not.
> +
> +	  If unsure, say N here.
> +
>  config PPC_COPRO_BASE
>  	bool
>  
> diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
> index 4ba303ea27f5..7cb6d18f5cd6 100644
> --- a/arch/powerpc/include/asm/mman.h
> +++ b/arch/powerpc/include/asm/mman.h
> @@ -40,8 +40,13 @@ static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
>  {
>  	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_SAO))
>  		return false;
> -	if ((prot & PROT_SAO) && !cpu_has_feature(CPU_FTR_SAO))
> -		return false;
> +	if (prot & PROT_SAO) {
> +		if (!cpu_has_feature(CPU_FTR_SAO))
> +			return false;
> +		if (firmware_has_feature(FW_FEATURE_LPAR) &&
> +		    !IS_ENABLED(CONFIG_PPC_PROT_SAO_LPAR))
> +			return false;
> +	}
>  	return true;
>  }
>  #define arch_validate_prot arch_validate_prot
> -- 
> 2.28.0
> 
>