[PATCH 1/6] firmware/smccc: Call arch-specific hook on discovering KVM services

[Will Deacon]

On Wed, Jul 31, 2024 at 08:11:16PM +0530, Aneesh Kumar K.V wrote:
> Will Deacon <will at kernel.org> writes:
> 
> > From: Marc Zyngier <maz at kernel.org>
> >
> > arm64 will soon require its own callback to initialise services
> > that are only available on this architecture. Introduce a hook
> > that can be overloaded by the architecture.
> >
> > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > Signed-off-by: Will Deacon <will at kernel.org>
> > ---
> >  arch/arm/include/asm/hypervisor.h   | 2 ++
> >  arch/arm64/include/asm/hypervisor.h | 4 ++++
> >  drivers/firmware/smccc/kvm_guest.c  | 2 ++
> >  3 files changed, 8 insertions(+)
> >
> > diff --git a/arch/arm/include/asm/hypervisor.h b/arch/arm/include/asm/hypervisor.h
> > index bd61502b9715..8a648e506540 100644
> > --- a/arch/arm/include/asm/hypervisor.h
> > +++ b/arch/arm/include/asm/hypervisor.h
> > @@ -7,4 +7,6 @@
> >  void kvm_init_hyp_services(void);
> >  bool kvm_arm_hyp_service_available(u32 func_id);
> >  
> > +static inline void kvm_arch_init_hyp_services(void) { };
> > +
> >  #endif
> > diff --git a/arch/arm64/include/asm/hypervisor.h b/arch/arm64/include/asm/hypervisor.h
> > index 0ae427f352c8..8cab2ab535b7 100644
> > --- a/arch/arm64/include/asm/hypervisor.h
> > +++ b/arch/arm64/include/asm/hypervisor.h
> > @@ -7,4 +7,8 @@
> >  void kvm_init_hyp_services(void);
> >  bool kvm_arm_hyp_service_available(u32 func_id);
> >  
> > +static inline void kvm_arch_init_hyp_services(void)
> > +{
> > +};
> > +
> >  #endif
> > diff --git a/drivers/firmware/smccc/kvm_guest.c b/drivers/firmware/smccc/kvm_guest.c
> > index 89a68e7eeaa6..f3319be20b36 100644
> > --- a/drivers/firmware/smccc/kvm_guest.c
> > +++ b/drivers/firmware/smccc/kvm_guest.c
> > @@ -39,6 +39,8 @@ void __init kvm_init_hyp_services(void)
> >  
> >  	pr_info("hypervisor services detected (0x%08lx 0x%08lx 0x%08lx 0x%08lx)\n",
> >  		 res.a3, res.a2, res.a1, res.a0);
> > +
> > +	kvm_arch_init_hyp_services();
> >  }
> >
> 
> That is a bit late to detect RMM? One of the requirements is to
> figure out the pgprot_t flags for early_ioremap so that "earlycon" will
> work (by mapping the address as shared alias). To do that we need to
> make an RSI call to detect PROT_NS_SHARED mask as below. 
> 
> 	if (rsi_get_realm_config(&config))
> 		return;
> 	prot_ns_shared = BIT(config.ipa_bits - 1);

Why can't the earlycon MMIO address just have that high bit set?

I think it's horribly fragile to try detecting all of this stuff before
we're allowed to touch the console. We don't even bother with pKVM --
it's the guest firmware's responsibility to MMIO_GUARD the UART if it
detects a debuggable payload.

Will