From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AEFE5308F32; Tue, 4 Aug 2026 08:50:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785833417; cv=none; b=tZwB1wcaHpBO91p/0bCGPiLdshQkXPrd9eFqtkj9/KxTq4pMP2fWRwWBHh46wMiC3/CUm7kFghOj74UZsl51wf2QPJ0K8MV0MxebT1lXJwYKTY/LPYHxvVNMVy9ikPdkpGtZ5b/wPBWiSG29lAWA/rAymdOf4hfVR+C935VRwDA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785833417; c=relaxed/simple; bh=VcHnWDriYeddWLcOQ0hYalcfh87LwCkbuu62RlcfYbA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ioRvXf1o6gQq5XwGyS2SdO0D1qdO47mkLmwHC0rl5z17eR7COmILYlxODoJwCc9wNIR6BJiQ+cgAnkWePXXf4sdsVgNqk9uEXcLM2+tc3W3Lw7crWqBmqSaG6W+FTtgpqb5lJRJKtIoLkHn2d8u3nIuMZmMjLPL8u4/WcfPN9aE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=PWSJKcRC; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="PWSJKcRC" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A62681476; Tue, 4 Aug 2026 01:50:09 -0700 (PDT) Received: from [192.168.178.24] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4CA673F66F; Tue, 4 Aug 2026 01:50:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785833413; bh=VcHnWDriYeddWLcOQ0hYalcfh87LwCkbuu62RlcfYbA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PWSJKcRCSX0elqSMxsjddTtGmAlvRcixtZ+JoG8sAF8m4eo/I4WLI+/QMrmrJWn9W PrZAyfr4fSVkhWtfWwnZvn95f3c70KdoIj55O9P/imylHXiZsdPMV0nLcq9uxF5INK TdnSmi0AS3VCS4dwVExE3dLgoO4bmM3Vga/PN3/o= Message-ID: Date: Tue, 4 Aug 2026 10:50:08 +0200 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 v7 00/11] arm_mpam: Add MPAM-Fb firmware support To: Gavin Shan , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , "Rafael J . Wysocki" , Len Brown , James Morse , Ben Horgan , Reinette Chatre , Fenghua Yu Cc: Jonathan Cameron , Srivathsa L Rao , Ganapatrao Kulkarni , Trilok Soni , Srinivas Ramana , Niyas Sait , Lee Trager , Ritwick Sharma , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260731170324.2927758-1-andre.przywara@arm.com> <6f8bc358-91a0-4c44-9110-c071e10df385@redhat.com> Content-Language: en-GB From: Andre Przywara In-Reply-To: <6f8bc358-91a0-4c44-9110-c071e10df385@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Gavin, many thanks for the review and the testing! ... On 8/4/26 05:29, Gavin Shan wrote: > On 8/1/26 3:03 AM, Andre Przywara wrote: >> v7 is another quick respin of the MPAM-Fb code, for firmware based MSC >> accesses. This propagates MSC access errors in a function where it was >> missing before, covering more functions that pass their return value >> to userspace (new patch 07/11). Also some bug fixes, formatting >> adjustments and adding the accumulated tags - many thanks to the >> reviewers. Find the changelog below. Based on v7.2-rc1. >> >> ======================= >> The Arm MPAM specification defines Memory System Components (MSCs), >> which are devices that are programmed through an MMIO register frame. In >> some occasions this turned out to be too limiting: the MSC might be >> located behind a separate bus system (for instance inside an on-board >> controller), it might be mapped secure-only, or in a different processor >> socket without direct MMIO mapping. Also the MMIO access might be too >> slow >> or it would need to be filtered or otherwise access controlled. Finally >> there might be bugs in the MSC integration, which require a mediating >> firmware to be accessible. >> >> To accommodate all those different use cases, the MPAM-Fb specification >> [1] describes an alternative way to access MSCs. Accesses to an MSC >> would be wrapped in a message and communicated to the system using a >> shared-memory/mailbox system mostly mimicking the Arm SCMI spec. >> For ACPI systems, this would be abstracted through an ACPI PCC channel, >> which provides the shared-memory region and the mailbox trigger. We can >> lean on existing ACPI parsing code to register with these two >> subsystems, but cannot rely on the existing SCMI code in the kernel. >> This means we somewhat need to open code a very simplified SCMI handler, >> which just provides enough functionality for the very basic subset of >> SCMI that the MPAM-Fb spec requires. >> >> The first seven patches rework all MSC access wrappers to propagate error >> information. Pure MMIO based MSC accesses would never fail, but the >> MPAM-Fb access can go wrong in multiple ways. The patches have been split >> up purely for reviewing reasons, if the number is a problem, we could as >> well squash them. Please note that until the very last patch of this >> series >> any MSC accesses would always only return 0, it's only the final >> enablement >> of MPAM-Fb that could possibly introduce errors. Hence all former patches >> can add error handling gradually, those code paths wouldn't be triggered >> before patch 11/11. >> Patch 8/11 solves a nasty problem: At the moment we protect stateful MSC >> register accesses (mon_sel) through a spinlock. Unfortunately the mailbox >> subsystem and the slow nature of the communication through this channel >> forbid MPAM-Fb access in atomic context. So this patch keeps using a >> spinlock for MMIO based accesses, but reverts to a mutex otherwise. >> We just deny taking the lock for MPAM-Fb in atomic context, ideally we >> wouldn't need that (no need to IPI another core when the MSC access does >> not need to be local to one particular core), or we simply deny that part >> of the functionality (access through perf). >> Patch 9/11 adds the code to redirect MSC accesses through the >> PCC shmem/mailbox system. >> Patch 10/11 reworks the error interrupt handler to use a threaded IRQ for >> MPAM-Fb, to be able to do MPAM-Fb MSC accesses inside (which might >> sleep). >> The final patch 11/11 then adds the code to detect and store the PCC >> channel information from the ACPI tables, and eventually enables >> MPAM-Fb accesses. >> >> This would enable systems where some MSCs are not accessible via MMIO to >> use those components anyway. >> >> Please have a look and test! >> >> Cheers, >> Andre >> >> [1] https://developer.arm.com/documentation/den0144/latest >> >> Changes in v7: >> - add tags >> - add new patch to propagate errors in mpam_reprogram_ris_partid() >> - prevent loop when mpam_diable() tries MSC accesses again >> - register MMIO error IRQ handler without IRQF_ONESHOT >> - re-use existing "err" variable instead of declaring "ret" >> - initialise mon_sel_lock later, to wait for interface decision >> - convert timeout units for nominal latency, between us and ms > > [...] > >> >> Andre Przywara (11): >>    arm_mpam: let low level MSC accessors return an error >>    arm_mpam: propagate MSC access errors for hw_probe functions >>    arm_mpam: propagate MSC access errors for MBWU counters >>    arm_mpam: propagate MSC access errors for msmon helpers >>    arm_mpam: propagate MSC access errors for __ris_msmon_read() >>    arm_mpam: propagate MSC access errors for state saving function >>    arm_mpam: propagate MSC access errors for mpam_reprogram_ris_partid() >>    arm_mpam: prepare mon_sel locking for MPAM-Fb >>    arm_mpam: add MPAM-Fb MSC firmware access support >>    arm_mpam: change MPAM-Fb error IRQ to use a threaded IRQ handler >>    arm_mpam: detect and enable MPAM-Fb PCC support >> >>   drivers/resctrl/Makefile        |   2 +- >>   drivers/resctrl/mpam_devices.c  | 820 +++++++++++++++++++++++--------- >>   drivers/resctrl/mpam_fb.c       | 250 ++++++++++ >>   drivers/resctrl/mpam_internal.h |  62 ++- >>   include/linux/arm_mpam.h        |   2 +- >>   5 files changed, 915 insertions(+), 221 deletions(-) >>   create mode 100644 drivers/resctrl/mpam_fb.c >> > > With this series (manually) applied to v7.2.rc6, the tests for the > existing functions > like kunit-tests, L3 cache partitioning, MBW (soft) limiting, > llc_occupancy monitor > look fine on NVidia's grace-hopper machine. Awesome, many thanks for doing that! > Tested-by: Gavin Shan I'd assume this is a regression test, as your machine uses the standard MMIO interface? If you don't mind, I'd put this tag on the first refactoring patches, so 01/11 - 08/11, and leave out the remaining 3, as they are about MPAM-Fb, which wasn't really tested, I guess? Also patch 10/11 (the error IRQ changes) changed, so I would drop all tags from this anyway. Cheers, Andre