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Mon, 02 Mar 2026 17:52:11 +0000 Date: Mon, 02 Mar 2026 17:52:10 +0000 Message-ID: <86o6l686gl.wl-maz@kernel.org> From: Marc Zyngier 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, gshan@redhat.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, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev, zengheng4@huawei.com, linux-doc@vger.kernel.org, Shaopeng Tan Subject: Re: [PATCH v5 02/41] KVM: arm64: Preserve host MPAM configuration when changing traps In-Reply-To: <20260224175720.2663924-3-ben.horgan@arm.com> References: <20260224175720.2663924-1-ben.horgan@arm.com> <20260224175720.2663924-3-ben.horgan@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; 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SAEximRunCond expanded to false On Tue, 24 Feb 2026 17:56:41 +0000, Ben Horgan wrote: > > When kvm enables or disables MPAM traps to EL2 it clears all other bits in nit: s/kvm/KVM/g > 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. > > Tested-by: Gavin Shan > Tested-by: Shaopeng Tan > Tested-by: Peter Newman > Tested-by: Zeng Heng > Reviewed-by: Shaopeng Tan > Reviewed-by: Jonathan Cameron > Reviewed-by: Gavin Shan > Signed-off-by: Ben Horgan > --- > arch/arm64/kvm/hyp/include/hyp/switch.h | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h > index 2597e8bda867..0b50ddd530f3 100644 > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h > @@ -267,7 +267,8 @@ static inline void __deactivate_traps_hfgxtr(struct kvm_vcpu *vcpu) > > static inline void __activate_traps_mpam(struct kvm_vcpu *vcpu) > { > - u64 r = MPAM2_EL2_TRAPMPAM0EL1 | MPAM2_EL2_TRAPMPAM1EL1; > + u64 clr = MPAM2_EL2_EnMPAMSM; > + u64 set = MPAM2_EL2_TRAPMPAM0EL1 | MPAM2_EL2_TRAPMPAM1EL1; > > if (!system_supports_mpam()) > return; > @@ -277,18 +278,21 @@ static inline void __activate_traps_mpam(struct kvm_vcpu *vcpu) > write_sysreg_s(MPAMHCR_EL2_TRAP_MPAMIDR_EL1, SYS_MPAMHCR_EL2); > } else { > /* From v1.1 TIDR can trap MPAMIDR, set it unconditionally */ > - r |= MPAM2_EL2_TIDR; > + set |= MPAM2_EL2_TIDR; > } > > - write_sysreg_s(r, SYS_MPAM2_EL2); > + sysreg_clear_set_s(SYS_MPAM2_EL2, clr, set); > } > > static inline void __deactivate_traps_mpam(void) > { > + u64 clr = MPAM2_EL2_TRAPMPAM0EL1 | MPAM2_EL2_TRAPMPAM1EL1 | MPAM2_EL2_TIDR; > + u64 set = MPAM2_EL2_EnMPAMSM; > + > if (!system_supports_mpam()) > return; > > - write_sysreg_s(0, SYS_MPAM2_EL2); > + sysreg_clear_set_s(SYS_MPAM2_EL2, clr, set); > > if (system_supports_mpam_hcr()) > write_sysreg_s(MPAMHCR_HOST_FLAGS, SYS_MPAMHCR_EL2); Acked-by: Marc Zyngier M. -- Without deviation from the norm, progress is not possible.