KVM: arm64: Disable MPAM visibility by default, and handle traps

maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T2RT

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpam/snapshot/v6.7-rc2



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Currently KVM only allows writeable ID registers to be downgraded
in the 'safe' direction, as determined by the cpufeature 'lower safe'
flags.

commit 011e5f5b ("arm64/cpufeature: Add remaining feature bits in
ID_AA64PFR0 register") exposed the MPAM field of AA64PFR0_EL1 to guests,
but didn't add trap handling. A previous patch supplied the missing trap
handling.

Existing VMs that have the MPAM field of AA64PFR0_EL1 need to be
migratable, but there is little point enabling the MPAM CPU interface
on new VMs until there is something a guest can do with it.

Clear the MPAM field from the guest's AA64PFR0_EL1 by default, but
allow user-space to set it again if the host supports MPAM. Add a
helper to return the maximum permitted value for an ID register.
For most this is the reset value. To allow the MPAM field to be
written as supported, check if the host sanitised value is '1'
and upgrade the reset value.

Finally, change the trap handling to inject an undef if MPAM was
not advertised to the guest.

Full support will depend on an psuedo-device being created that
describes the virt->phys PARTID mapping the VMM expects. Migration
would be expected to fail if this psuedo-device can't be created
on the remote end. This ID bit isn't needed to block migration.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Zeng Heng <zengheng4@huawei.com>