On Tue, Jan 09, 2018 at 07:04:00PM +0000, Suzuki K Poulose wrote:
> Add a helper to convert ID_AA64MMFR0_EL1:PARange to they physical
                                                      *the*
> size shift. Limit the size to the maximum supported by the kernel.

Is this just a cleanup or are we actually going to need this feature in
the subsequent patches?  That would be nice to motivate in the commit
letter.

> 
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Cc: Will Deacon <will.dea...@arm.com>
> Cc: Marc Zyngier <marc.zyng...@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
> ---
>  arch/arm64/include/asm/cpufeature.h | 16 ++++++++++++++++
>  arch/arm64/kvm/hyp/s2-setup.c       | 28 +++++-----------------------
>  2 files changed, 21 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h 
> b/arch/arm64/include/asm/cpufeature.h
> index ac67cfc2585a..0564e14616eb 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -304,6 +304,22 @@ static inline u64 read_zcr_features(void)
>       return zcr;
>  }
>  
> +static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
> +{
> +     switch (parange) {
> +     case 0: return 32;
> +     case 1: return 36;
> +     case 2: return 40;
> +     case 3: return 42;
> +     case 4: return 44;
> +
> +     default:

What is the case we want to cater for with making parange == 5 the
default for unrecognized values?

(I have a feeling that default label comes from making the compiler
happy about potentially uninitialized values once upon a time before a
lot of refactoring happened here.)

> +     case 5: return 48;
> +#ifdef CONFIG_ARM64_PA_BITS_52
> +     case 6: return 52;
> +#endif
> +     }
> +}
>  #endif /* __ASSEMBLY__ */
>  
>  #endif
> diff --git a/arch/arm64/kvm/hyp/s2-setup.c b/arch/arm64/kvm/hyp/s2-setup.c
> index 603e1ee83e89..b1129c83c531 100644
> --- a/arch/arm64/kvm/hyp/s2-setup.c
> +++ b/arch/arm64/kvm/hyp/s2-setup.c
> @@ -19,11 +19,13 @@
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_hyp.h>
> +#include <asm/cpufeature.h>
>  
>  u32 __hyp_text __init_stage2_translation(void)
>  {
>       u64 val = VTCR_EL2_FLAGS;
>       u64 parange;
> +     u32 phys_shift;
>       u64 tmp;
>  
>       /*
> @@ -37,27 +39,7 @@ u32 __hyp_text __init_stage2_translation(void)
>       val |= parange << 16;
>  
>       /* Compute the actual PARange... */
> -     switch (parange) {
> -     case 0:
> -             parange = 32;
> -             break;
> -     case 1:
> -             parange = 36;
> -             break;
> -     case 2:
> -             parange = 40;
> -             break;
> -     case 3:
> -             parange = 42;
> -             break;
> -     case 4:
> -             parange = 44;
> -             break;
> -     case 5:
> -     default:
> -             parange = 48;
> -             break;
> -     }
> +     phys_shift = id_aa64mmfr0_parange_to_phys_shift(parange);
>  
>       /*
>        * ... and clamp it to 40 bits, unless we have some braindead
> @@ -65,7 +47,7 @@ u32 __hyp_text __init_stage2_translation(void)
>        * return that value for the rest of the kernel to decide what
>        * to do.
>        */
> -     val |= 64 - (parange > 40 ? 40 : parange);
> +     val |= 64 - (phys_shift > 40 ? 40 : phys_shift);
>  
>       /*
>        * Check the availability of Hardware Access Flag / Dirty Bit
> @@ -86,5 +68,5 @@ u32 __hyp_text __init_stage2_translation(void)
>  
>       write_sysreg(val, vtcr_el2);
>  
> -     return parange;
> +     return phys_shift;
>  }
> -- 
> 2.13.6
> 

Could you fold this change into the commit as well:

diff --git a/arch/arm64/kvm/hyp/s2-setup.c b/arch/arm64/kvm/hyp/s2-setup.c
index 603e1ee83e89..eea2fbd68b8a 100644
--- a/arch/arm64/kvm/hyp/s2-setup.c
+++ b/arch/arm64/kvm/hyp/s2-setup.c
@@ -29,7 +29,8 @@ u32 __hyp_text __init_stage2_translation(void)
        /*
         * Read the PARange bits from ID_AA64MMFR0_EL1 and set the PS
         * bits in VTCR_EL2. Amusingly, the PARange is 4 bits, while
-        * PS is only 3. Fortunately, bit 19 is RES0 in VTCR_EL2...
+        * PS is only 3. Fortunately, only three bits is actually used to
+        * enode the supported PARange values.
         */
        parange = read_sysreg(id_aa64mmfr0_el1) & 7;
        if (parange > ID_AA64MMFR0_PARANGE_MAX)


Thanks,
-Christoffer
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