Re: [PATCH 03/11] KVM: arm64: CCA: Check for RMI support at KVM init

[Kohei Enju]

On 11/04 10:39, Suzuki K Poulose wrote:
> Hi Kohei
> 
> On 04/11/2026 10:27, Kohei Enju wrote:
> > On 11/04 19:23, Kohei Enju wrote:
> > > Hi Steven,
> > > 
> > > On 11/02 14:12, Steven Price wrote:
> > > > Check if the RMI support is sufficient for using in KVM. Specifically, we
> > > > will only support creating realm VMs when KVM is set to 'rmm' mode.
> > > > 
> > > > Signed-off-by: Steven Price <steven.price@xxxxxxx>
> > > > ---
> > > >   arch/arm64/kvm/Kconfig | 1 +
> > > >   arch/arm64/kvm/rmi.c   | 4 +++-
> > > >   2 files changed, 4 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > > > index cecea0820e52..d067063a3686 100644
> > > > --- a/arch/arm64/kvm/Kconfig
> > > > +++ b/arch/arm64/kvm/Kconfig
> > > > @@ -34,6 +34,7 @@ menuconfig KVM
> > > >   	select GUEST_PERF_EVENTS if PERF_EVENTS
> > > >   	select KVM_GUEST_MEMFD
> > > >   	select KVM_GENERIC_PRE_FAULT_MEMORY
> > > > +	select ARM_RMM_RMI
> > > >   	help
> > > >   	  Support hosting virtualized guest machines.
> > > > diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
> > > > index 5ecc8b349869..9d118768550d 100644
> > > > --- a/arch/arm64/kvm/rmi.c
> > > > +++ b/arch/arm64/kvm/rmi.c
> > > > @@ -3,6 +3,7 @@
> > > >    * Copyright (C) 2023-2026 ARM Ltd.
> > > >    */
> > > > +#include <linux/arm-rmi-cmds.h>
> > > >   #include <linux/kvm_host.h>
> > > >   #include <asm/virt.h>
> > > > @@ -12,7 +13,8 @@ void kvm_init_rmi(void)
> > > >   	if (kvm_get_mode() != KVM_MODE_RMM)
> > > >   		return;
> > > > -	/* TODO: Check if the RMI is available */
> > > > +	if (!is_rmi_available())
> > > > +		return;
> > > 
> > >  From an admin/operator's perspective, kvm_rmi_is_available would
> > > silently remain FALSE in either of the following cases:
> > > - kvm-arm.mode=rmm is set, but RMI is not available for some reason.
> 
> We could add a kvm_info() message for this.
> 
> > > - RMI is available, but the admin forgot to set kvm-arm.mode=rmm.
> 
> But not this one. We are additionally planning to move the RMM
> activation to gate on kvm-arm.mode=rmm. I will send out a patch
> soon.

I wasn't aware of that plan. In that case, this scenario will be
unreachable, so I have no concerns.

Thanks,
Kohei