[PATCH v5 6/7] KVM: arm64: Disable MPAM visibility by default and ignore VMM writes

[Gavin Shan]

On 10/15/24 11:39 PM, Joey Gouly wrote:
> From: James Morse <james.morse at arm.com>
> 
> commit 011e5f5bf529f ("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 ID_AA64PFR0_EL1 set 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 ID_AA64PFR0_EL1 and on hardware
> that supports MPAM, politely ignore the VMMs attempts to set this bit.
> 
> Guests exposed to this bug have the sanitised value of the MPAM field,
> so only the correct value needs to be ignored. This means the field
> can continue to be used to block migration to incompatible hardware
> (between MPAM=1 and MPAM=5), and the VMM can't rely on the field
> being ignored.
> 
> Signed-off-by: James Morse <james.morse at arm.com>
> Co-developed-by: Joey Gouly <joey.gouly at arm.com>
> Signed-off-by: Joey Gouly <joey.gouly at arm.com>
> ---
>   arch/arm64/kvm/sys_regs.c | 44 ++++++++++++++++++++++++++++++++++++---
>   1 file changed, 41 insertions(+), 3 deletions(-)
> 

Reviewed-by: Gavin Shan <gshan at redhat.com>