linux-kernel - Re: [kvmtool test PATCH 22/24] kvmtool: arm64: Add support for guest physical address size

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Date:   Wed, 4 Jul 2018 15:09:43 +0100
From:   Will Deacon <will.deacon@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        james.morse@....com, marc.zyngier@....com, cdall@...nel.org,
        eric.auger@...hat.com, julien.grall@....com,
        catalin.marinas@....com, punit.agrawal@....com,
        qemu-devel@...gnu.org
Subject: Re: [kvmtool test PATCH 22/24] kvmtool: arm64: Add support for guest
 physical address size

On Fri, Jun 29, 2018 at 12:15:42PM +0100, Suzuki K Poulose wrote:
> Add an option to specify the physical address size used by this
> VM.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  arm/aarch64/include/kvm/kvm-config-arch.h | 5 ++++-
>  arm/include/arm-common/kvm-config-arch.h  | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
> index 04be43d..dabd22c 100644
> --- a/arm/aarch64/include/kvm/kvm-config-arch.h
> +++ b/arm/aarch64/include/kvm/kvm-config-arch.h
> @@ -8,7 +8,10 @@
>  			"Create PMUv3 device"),				\
>  	OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed,			\
>  			"Specify random seed for Kernel Address Space "	\
> -			"Layout Randomization (KASLR)"),
> +			"Layout Randomization (KASLR)"),		\
> +	OPT_INTEGER('\0', "phys-shift", &(cfg)->phys_shift,		\
> +			"Specify maximum physical address size (not "	\
> +			"the amount of memory)"),

Given that this is a shift value, I think the help message could be more
informative. Something like:

	"Specify maximum number of bits in a guest physical address"

I think I'd actually leave out any mention of memory, because this does
actually have an effect on the amount of addressable memory in a way that I
don't think we want to describe in half of a usage message line :)

Will