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Wed, 14 Jan 2026 12:09:15 +0000 Date: Wed, 14 Jan 2026 12:09:14 +0000 Message-ID: <86o6mwl7kl.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 Subject: Re: [PATCH v3 13/47] KVM: arm64: Use kernel-space partid configuration for hypercalls In-Reply-To: <20260112165914.4086692-14-ben.horgan@arm.com> References: <20260112165914.4086692-1-ben.horgan@arm.com> <20260112165914.4086692-14-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; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: ben.horgan@arm.com, 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 X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Mon, 12 Jan 2026 16:58:40 +0000, Ben Horgan wrote: > > On nVHE systems whether or not MPAM is enabled, EL2 continues to use > partid-0 for hypercalls, even when the host may have configured its kernel > threads to use a different partid. 0 may have been assigned to another > task. Copy the EL1 MPAM register to EL2. This ensures hypercalls use the > same partid as the kernel thread does on the host. > > Signed-off-by: Ben Horgan > --- > Changes since v2: > Use mask > Use read_sysreg_el1 to cope with hvhe > --- > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index a7c689152f68..ad99d8a73a9e 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -635,6 +635,14 @@ static void handle_host_hcall(struct kvm_cpu_context *host_ctxt) > unsigned long hcall_min = 0; > hcall_t hfn; > > + if (system_supports_mpam()) { > + u64 mask = MPAM1_EL1_PARTID_D | MPAM1_EL1_PARTID_I | > + MPAM1_EL1_PMG_D | MPAM1_EL1_PMG_I; > + > + write_sysreg_s(read_sysreg_el1(SYS_MPAM1) & mask, SYS_MPAM2_EL2); > + isb(); > + } Is it really OK to not preserve the rest of MPAM2_EL2? This explicitly clears MPAM2_EL2.MPAMEN, which feels counter-productive. M. -- Without deviation from the norm, progress is not possible.