RE: [PATCH v7 00/45] arm64: Support for Arm CCA in KVM

Emi Kisanuki (Fujitsu)
2025-04-01T06:55:59Z

> Hi Emi,
>
> On Wed, Mar 26, 2025 at 02:14:35AM +0000, Emi Kisanuki (Fujitsu) wrote:
> > Hi all,
> >
> > I tested Linux-cca cca-host/v7 patch with our Internal simulator based on
> QEMU (with CCA and MPAM support).
> > A panic occurred when starting Realm, but I don't think this is a problem with the
> cca-host/v7 patch.
> > The location of the panic is [1].
> >
> > [1]https://lore.kernel.org/linux-arm-kernel/20241030160317.2528209-4-j
> > oey.gouly@arm.com diff --git a/arch/arm64/kernel/cpuinfo.c
> > b/arch/arm64/kernel/cpuinfo.c index 44718d0482b3..46ba30d42b9b 100644
> > --- a/arch/arm64/kernel/cpuinfo.c
> > +++ b/arch/arm64/kernel/cpuinfo.c
> > @@ -478,6 +478,9 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64
> *info)
> > if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
> > __cpuinfo_store_cpu_32bit(&info->aarch32);
> >
> > + if (id_aa64pfr0_mpam(info->reg_id_aa64pfr0))
> > + info->reg_mpamidr = read_cpuid(MPAMIDR_EL1); ///////
> panic occurred here.
> > +
> > cpuinfo_detect_icache_policy(info);
> > }
> >
> > There was no problem with the cca-host/v5 patch (based on v6.12).
> > This panic is caused by accessing MPAMIDR_EL1 when the chip supports
> MPAM.
> > This functionality was enabled when the cca host patch base version was
> rebased from v6.12 to v6.13.
> >
> > I am not familiar with TF-A, but I think this maybe a TF-A's bug.
> > Because It seems TF-A sets MPAM3_EL3.TRAPLOWER to 0 during normal
> guest boot in manage_extensions_nonsecure_per_world function[2].
> > However, TF-A does not set it to 0 during Realm guest boot in
> manage_extensions_secure_per_world function.
> > Therefore, a trap occurs against EL3 (TF-A), and it is likely being processed as
> an invalid instruction (Undef).
>
> Your instinct is correct that this is *not* a kernel bug. It is the responsibility of the
> RMM to provide a consistent feature set to the Realm.
>
> Looks like this was addressed recently in TF-RMM by hiding FEAT_MPAM:
>
> https://github.com/TF-RMM/tf-rmm/commit/7b0874403726d215c40054abfd5d
> 8704049f8dac
>
> Thanks,
> Oliver

Hi Oliver
Thank you.
We will backport the patch you mentioned.

I have verified the following
1. Launching the realm VM using Internal simulator → Successfully launched by disabling MPAM support in the ID register.
2. Running kvm-unit-tests (with lkvm) → All tests passed except for PMU (as expected, since PMU is not supported by the Internal simulator).[1]

Tested-by: Emi Kisanuki <fj0570is@fujitsu.com>
[1] https://gitlab.arm.com/linux-arm/kvm-unit-tests-cca cca/v3

Best Regards,
Emi Kisanuki