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

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Message-ID: <20260105164352.00001e3c@huawei.com>
Date: Mon, 5 Jan 2026 16:43:52 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Ben Horgan <ben.horgan@....com>
CC: <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
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Subject: Re: [PATCH v2 05/45] KVM: arm64: Preserve host MPAM configuration
 when changing traps

On Fri, 19 Dec 2025 18:11:07 +0000
Ben Horgan <ben.horgan@....com> 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@....com>
Seems to match what I'd expect from the spec, so LGTM.
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>