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The ID_AA64PFR0.MPAM bit was previously accidentally exposed to guests, and is ignored by KVM. KVM will always present the guest with 0 here, and trap the MPAM system registers to inject an undef. But, this value is still needed to prevent migration when the value is incompatible with the target hardware. Add a kvm unit test to try and write multiple values to ID_AA64PFR0.MPAM. Only the hardware value previously exposed should be ignored, all other values should be rejected. Signed-off-by: James Morse <james.morse@arm.com> Signed-off-by: Joey Gouly <joey.gouly@arm.com> Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> Reviewed-by: Gavin Shan <gshan@redhat.com> Reviewed-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20241030160317.2528209-8-joey.gouly@arm.com Signed-off-by: Oliver Upton <oliver.upton@linux.dev>