Re: [PATCH v17 06/20] KVM: arm64: CCA: Add a new mode for supporting Realm guests

[Kohei Enju <enju.kohei@fujitsu.com>]

Hi Marc,

On 09/09 11:48, Marc Zyngier wrote:
> On Wed, 09 Sep 2026 04:26:41 +0100,
> Kohei Enju <enju.kohei@fujitsu.com> wrote:
> > 
> > Hi Suzuki,
> > 
> > On 09/08 17:22, Suzuki K Poulose wrote:
> > > Add an explicit mode to support Arm CCA guests.
> > > 
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > ---
> > >  Documentation/admin-guide/kernel-parameters.txt | 3 +++
> > >  arch/arm64/include/asm/kvm_host.h               | 1 +
> > >  arch/arm64/kvm/arm.c                            | 5 +++++
> > >  3 files changed, 9 insertions(+)
> > > 
> > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > index 68647ff4bdd24..1afe3df3b923e 100644
> > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > @@ -3256,6 +3256,9 @@ Kernel parameters
> > >  			nested: VHE-based mode with support for nested
> > >  				virtualization. Requires at least ARMv8.4
> > >  				hardware (with FEAT_NV2).
> > > +			rmm: Support for running confidential guests in Realm
> > > +			     world using RMM, as defined by Arm Confidential
> > > +			     Compute Architecture (CCA)
> > >  
> > >  			Defaults to VHE/nVHE based on hardware support. Setting
> > >  			mode to "protected" will disable kexec and hibernation
> > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > > index b2e99c5cb1cd3..31ae9d8d8e92f 100644
> > > --- a/arch/arm64/include/asm/kvm_host.h
> > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > @@ -69,6 +69,7 @@ enum kvm_mode {
> > >  	KVM_MODE_DEFAULT,
> > >  	KVM_MODE_PROTECTED,
> > >  	KVM_MODE_NV,
> > > +	KVM_MODE_RMM,
> > >  	KVM_MODE_NONE,
> > >  };
> > >  #ifdef CONFIG_KVM
> > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > > index 9af3bbb2f8c24..50f0adfadab38 100644
> > > --- a/arch/arm64/kvm/arm.c
> > > +++ b/arch/arm64/kvm/arm.c
> > > @@ -3264,6 +3264,11 @@ static int __init early_kvm_mode_cfg(char *arg)
> > >  		return 0;
> > >  	}
> > >  
> > > +	if (strcmp(arg, "rmm") == 0 && !WARN_ON(!is_kernel_in_hyp_mode())) {
> > > +		kvm_mode = KVM_MODE_RMM;
> > > +		return 0;
> > > +	}
> > 
> > Does this make NV support and CCA Realm VM support mutually exclusive?
> > 
> > Until the v16 series, we could run Realm VMs with:
> >   'kvm-arm.mode=nested'
> > 
> > As far as the AArch64 architecture is concerned, there does not seem to
> > be a reason to make them mutually exclusive. I am therefore wondering
> > whether this restriction is intentional.
> 
> I have a hack somewhere that will allow this, but this requires to
> change the above to be a capability mask rather than a simple
> enumeration. I'll see if I can spin that as a separate series.

Ack. Thank you for the clarification.
Looking forward to seeing the series.

Thanks,
Kohei

> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.