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Wed, 14 Jan 2026 18:33:46 -0800 (PST) Message-ID: Date: Thu, 15 Jan 2026 10:33:33 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 04/47] KVM: arm64: Preserve host MPAM configuration when changing traps To: Ben Horgan Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, carl@os.amperecomputing.com, dave.martin@arm.com, david@kernel.org, dfustini@baylibre.com, fenghuay@nvidia.com, james.morse@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peternewman@google.com, punit.agrawal@oss.qualcomm.com, quic_jiles@quicinc.com, reinette.chatre@intel.com, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, tan.shaopeng@fujitsu.com, xhao@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, corbet@lwn.net, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev References: <20260112165914.4086692-1-ben.horgan@arm.com> <20260112165914.4086692-5-ben.horgan@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260112165914.4086692-5-ben.horgan@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/13/26 12:58 AM, Ben Horgan 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. > > Reviewed-by: Jonathan Cameron > Signed-off-by: Ben Horgan > --- > arch/arm64/kvm/hyp/include/hyp/switch.h | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > Reviewed-by: Gavin Shan