Re: [PATCH v7 9/10] KVM: arm64: docs: document KVM support of pointer authentication

[Amit Daniel Kachhap]

Hi Dave,

On 3/27/19 7:20 PM, Dave Martin wrote:
> On Wed, Mar 27, 2019 at 05:19:28PM +0530, Amit Daniel Kachhap wrote:
> > Hi,
> >
> > On 3/27/19 4:14 PM, Dave Martin wrote:
> > > On Mon, Mar 25, 2019 at 08:05:49PM +0000, Kristina Martsenko wrote:
> > > > On 19/03/2019 08:30, Amit Daniel Kachhap wrote:
> > > > > This adds sections for KVM API extension for pointer authentication.
> > > > > A brief description about usage of pointer authentication for KVM guests
> > > > > is added in the arm64 documentations.
> > > > >
> > > > > Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
> > > > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > > > Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> > > > > Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> > > > > Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
> > > >
> > > > I think it makes sense to also update the Kconfig symbol description for
> > > > CONFIG_ARM64_PTR_AUTH, since it currently only mentions userspace
> > > > support, but now the option also enables KVM guest support.
> > > >
> > > > It's also worth mentioning that CONFIG_ARM64_VHE=y is required for guest
> > > > support.
> > >
> > > Is it worth making this dependency explicit in Kconfig?
> > Currently there is discrepancy that userspace supports ptrauth in both
> > nVHE/VHE mode and KVM guest only in VHE mode. I suppose adding explicit
> > dependency flag here makes both of them similar.
>
> Looking at the history, for SVE this Kconfig restriction has always been
> present.  Since ptrauth initially upstreamed without an equivalent
> restriction in Kconfig, adding it now could be seen as a regression.
ok it makes sense to keep it this way.
> So, maybe it's not worth it here.
>
> You could add a separate option, say
>
> config ARM64_PTR_AUTH_KVM
> 	bool "Pointer authentication support for KVM guests"
> 	default y
> 	depends on ARM64_PTR_AUTH && ARM64_VHE && KVM
>
> ...but that may be overkill.
I was thinking for adding some details for this in virtualization 
section in Documentation/arm64/pointer-authentication.txt along with 
brief comment in arch/arm64/Kconfig.

Thanks,
Amit D
> Cheers,
> ---Dave