From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DB1D27E0E8; Fri, 19 Dec 2025 20:01:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766174493; cv=none; b=lJcdq5B4BvZPwtOVQW1PQWnXx481EMnXyK7KbdhQm7ul2+A4lFAz3hPPomgHNmVy06NLSsUZyXxWxI9x3+2BkxRELxzyzOA+vmDG2xrBFeUpqbL+yvqd+w7/Wbi2Y4pNAdHd1i57gy4dxGcIf5x0neyTNxW75pAaigekS3kd2Pk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766174493; c=relaxed/simple; bh=8pUZmGCDJ1FRjMBboLacZFWGbm4ILMwIQXmKN3FO6Ao=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=o5uF355IdE6uJ4PZFeYZ9qoMzm9ZMNy7n5QVgEQHc/eOEzQjb+mfCOZ9jB0Am8utEeltZGSkcUj8YA7VknzACfCgmgt0p5AvHVcANePZI/yeQlnIwwiHm27XrTviPwq/AsiCC+KKJh/N/s86YZmlRDl99+Th1UPCuiahEaYJf+o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=r0sXO6BT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="r0sXO6BT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C417C4CEF1; Fri, 19 Dec 2025 20:01:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766174492; bh=8pUZmGCDJ1FRjMBboLacZFWGbm4ILMwIQXmKN3FO6Ao=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r0sXO6BT/vcNQGDrlB9yBfVJqM3igby0cJbL1l7VI6hqkx+rcosg37YWD5nBa4oXk jL5voRf92E0kYiIhGXQkB01F/PuPRT2zQDHjK3pP6M2K77IDVHr5xgx6Wb8/a17QeS YpO3PZTSpa0drljnYZdeZW/9kGCqacQxrr0WtKv0OFK2CB4C1dddB0lqZ1GIVed3nW 2r4LMfMJvdTEoy6+/azwDLAiv3VhYTMro/lg8Cs8Qtaa34pLaYGtSADdrp42wTmMbp KC96hXht+fPuZju0WMp4q4QLqRlbSxkowxodLa3gF39b1I6DsTOFSuXZkNvFfEJn9N OJYwXBH/I5URA== Date: Fri, 19 Dec 2025 12:01:30 -0800 From: Oliver Upton 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, maz@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev Subject: Re: [PATCH v2 05/45] KVM: arm64: Preserve host MPAM configuration when changing traps Message-ID: References: <20251219181147.3404071-1-ben.horgan@arm.com> <20251219181147.3404071-6-ben.horgan@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251219181147.3404071-6-ben.horgan@arm.com> Hi Ben, On Fri, Dec 19, 2025 at 06:11:07PM +0000, 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. > > 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 c5d5e5b86eaf..63195275a8b8 100644 > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h > @@ -269,7 +269,8 @@ 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; > @@ -279,18 +280,21 @@ 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); I'd recommend documenting that writes to MPAM1_EL1 are followed by an ISB. Otherwise it isn't obvious here where context synchronization is happening (if at all). Thanks, Oliver