Subject: Re: [PATCH 3/3] Enable storage keys for radix - user mode execution

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 08 Nov 2016 21:45:36 +0530

Balbir Singh <[email-masked]> writes:

> ISA 3 defines new encoded access authority that allows instruction
> access prevention in privileged mode and allows normal access
> to problem state. This patch just enables IAMR (Instruction Authority
> Mask Register), enabling AMR would require more work.

We may want to explain what the rules are with details like IAMR class 0
bit 1 controls the instruction access etc. Also we can metion that we
now setup user pages such that EAA[0] is set to 0

>
> I've tested this with a buggy driver and a simple payload. The payload
> is specific to the build I've tested.
>
> Signed-off-by: Balbir Singh <[email-masked]>
> ---
>  arch/powerpc/mm/pgtable-radix.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
> index 0fdd8ed..cd3d400 100644
> --- a/arch/powerpc/mm/pgtable-radix.c
> +++ b/arch/powerpc/mm/pgtable-radix.c
> @@ -339,6 +339,24 @@ static void __init radix_init_amor(void)
>  	mtspr(SPRN_AMOR, amor);
>  }
>  
> +/*
> + * For radix page tables we setup, the IAMR values as follows
> + * IMAR = 0100...00 (key 0 is set to 1)
> + * AMR, UAMR, UAMOR are not affected
> + */
> +static void __init radix_init_iamr(void)
> +{
> +	unsigned long iamr_mask = 0x4000000000000000;
> +	unsigned long iamr = mfspr(SPRN_IAMR);
> +
> +	if (cpu_has_feature(CPU_FTR_POWER9_DD1))
> +		return;

is this needed ?

> +
> +	iamr |= iamr_mask;
> +
> +	mtspr(SPRN_IAMR, iamr);
> +}

Why do '|'. Who else can set this ?

> +
>  void __init radix__early_init_mmu(void)
>  {
>  	unsigned long lpcr;
> @@ -398,6 +416,7 @@ void __init radix__early_init_mmu(void)
>  		radix_init_amor();
>  	}
>  
> +	radix_init_iamr();
>  	radix_init_pgtable();
>  }

What about secondary cpus ?

-aneesh