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

[Julien Grall]

Hi,

On 04/07/18 15:09, Will Deacon wrote:
> 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@xxxxxxx>
> > ---
> >   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 :)
Is there any particular reasons to expose this option to the user?

I have recently sent a series to allow the user to specify the position
of the RAM [1]. With that series in mind, I think the user would not 
really need to specify the maximum physical shift. Instead we could 
automatically find it.

Cheers,

[1] 
http://archive.armlinux.org.uk/lurker/message/20180510.140428.1c295b5b.en.html

> Will

--
Julien Grall