Re: [PATCH v2 05/45] KVM: arm64: Preserve host MPAM configuration when changing traps

[Jonathan Cameron]

On Fri, 19 Dec 2025 18:11:07 +0000
Ben Horgan <ben.horgan@xxxxxxx> wrote:

> When kvm enables or disables MPAM traps to EL2 it clears all other bits in
> MPAM2_EL2.  Notably, it clears the partition ids (PARTIDs) and performance
> monitoring groups (PMGs). Avoid changing these bits in anticipation of
> adding support for MPAM in the kernel. Otherwise, on a VHE system with the
> host running at EL2 where MPAM2_EL2 and MPAM1_EL1 access the same register,
> any attempt to use MPAM to monitor or partition resources for kernel space
> would be foiled by running a KVM guest. Additionally, MPAM2_EL2.EnMPAMSM is
> always set to 0 which causes MPAMSM_EL1 to always trap. Keep EnMPAMSM set
> to 1 when not in a guest so that the kernel can use MPAMSM_EL1.
> 
> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
Seems to match what I'd expect from the spec, so LGTM.
Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>