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

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

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@arm.com>
> > ---
> >  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.
> - RMI is available, but the admin forgot to set kvm-arm.mode=rmm.
> 
> So I think it would be useful to emit diagnostic messages for these
> cases, for example:
> 
> if (!is_rmi_available()) {
>     if (kvm_get_mode() == KVM_MODE_RMM)
>         pr_info("Realm VM support is disabled because RMI is not available\n");
> 	return;
> }
> 
> if (kvm_get_mode() != KVM_MODE_RMM) {
>     pr_info("Realm VM support is disabled. Use kvm-arm.mode=rmm to enable it\n");
> 	return;
> }

Sorry, the indentation got mangled :(

> 
> Thanks,
> Kohei