Re: [kvmtool PATCH v10 5/5] KVM: arm/arm64: Add a vcpu feature for pointer authentication

[Amit Daniel Kachhap]

Hi Dave,

On 5/28/19 3:41 PM, Dave Martin wrote:
> On Wed, Apr 24, 2019 at 02:41:21PM +0100, Dave Martin wrote:
> > On Wed, Apr 24, 2019 at 12:32:22PM +0530, Amit Daniel Kachhap wrote:
> > > Hi,
> > >
> > > On 4/23/19 9:16 PM, Dave Martin wrote:
>
> [...]
>
> > > > > diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
> > > > > index 7780251..acd1d5f 100644
> > > > > --- a/arm/kvm-cpu.c
> > > > > +++ b/arm/kvm-cpu.c
> > > > > @@ -68,6 +68,18 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
> > > > >   		vcpu_init.features[0] |= (1UL << KVM_ARM_VCPU_PSCI_0_2);
> > > > >   	}
> > > > > +	/* Check Pointer Authentication command line arguments. */
> > > > > +	if (kvm->cfg.arch.enable_ptrauth && kvm->cfg.arch.disable_ptrauth)
> > > > > +		die("Both enable-ptrauth and disable-ptrauth option cannot be present");
> > > >
> > > > Preferably, print the leading dashes, the same as the user would see
> > > > on the command line (e.g., --enable-ptrauth, --disable-ptrauth).
> > > >
> > > > For brevity, we could write something like:
> > > >
> > > > 		die("--enable-ptrauth conflicts with --disable-ptrauth");
>
> [...]
>
> > > > > @@ -106,8 +118,12 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
> > > > >   			die("Unable to find matching target");
> > > > >   	}
> > > > > -	if (err || target->init(vcpu))
> > > > > -		die("Unable to initialise vcpu");
> > > > > +	if (err || target->init(vcpu)) {
> > > > > +		if (kvm->cfg.arch.enable_ptrauth)
> > > > > +			die("Unable to initialise vcpu with pointer authentication feature");
> > > >
> > > > We don't special-case this error message for any other feature yet:
> > > > there are a variety of reasons why we might have failed, so suggesting
> > > > that the failure is something to do with ptrauth may be misleading to
> > > > the user.
> > > >
> > > > If we want to be more informative, we could do something like the
> > > > following:
> > > >
> > > > 	bool supported;
> > > >
> > > > 	supported = kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> > > > 		    kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC);
> > > >
> > > > 	if (kvm->cfg.arch.enable_ptrauth && !supported)
> > > > 		die("--enable-ptrauth not supported on this host");
> > > >
> > > > 	if (supported && !kvm->cfg.arch.disable_ptrauth)
> > > > 		vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
> > > >
> > > > 	/* ... */
> > > >
> > > > 	if (err || target->init(vcpu))
> > > > 		die("Unable to initialise vcpu");
> > > >
> > > > We don't do this for any other feature today, but since it helps the
> > > > user to understand what went wrong it's probably a good idea.
> > > Yes this is more clear. As Mark has picked the core guest ptrauth patches. I
> > > will post this changes as standalone.
> >
> > Sounds good.  (I also need to do that separately for SVE...)
>
> Were you planning to repost this?
>
> Alternatively, I can fix up the diagnostic messages discussed here and
> post it together with the SVE support.  I'll do that locally for now,
> but let me know what you plan to do.  I'd like to get the SVE support
> posted soon so that people can test it.
I will clean up the print messages as you suggested and repost it shortly.

Thanks,
Amit Daniel
> Cheers
> ---Dave