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 DAD8E2D2397 for ; Fri, 17 Apr 2026 16:07:54 +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=1776442077; cv=none; b=iiDJKfdwqm6jRTgMAne04A7HKIskriMKDGjB29EpnEjx7jxC76Wch4U1hwIEIiwfsDvLYStvyYuzYNf+3AqAwZ90foSQ4+fpj53BJx+q2BDOsYZ7QkwWxfSdq/869JHQ9pQgqLLujsLUN3n0/y6Cyc5yowrQwemxU3+02Id2z28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776442077; c=relaxed/simple; bh=RCF6h9NDHm5JONWvfZWOyR4Ft2MZlkN74FF/O5IHdyY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=M4PyEwgdxq0iYMOxHIVnw/3sjQPcrS3bHDkjXyqrQuzfZ8jxBdBNUMCfUhZjhYlX/gfdrkQ+8UAMhGSVmnpkGbz61uEAdjoaVbaHNY+2IAwGhPAigdglTFvok2rWN89r409C4c0k47r/YAgQwrTQpGL03WN5/HmZ9C3c8J5kj2c= 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=ZqoSTvzQ; 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="ZqoSTvzQ" 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 620A11DB5; Fri, 17 Apr 2026 09:07:48 -0700 (PDT) Received: from [10.1.196.96] (eglon.cambridge.arm.com [10.1.196.96]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 62A9A3F641; Fri, 17 Apr 2026 09:07:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776442074; bh=RCF6h9NDHm5JONWvfZWOyR4Ft2MZlkN74FF/O5IHdyY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZqoSTvzQb12XLfbv7AT0hGIaSivur4BV76sHByTOWgASVb8M49Ywsyusr+d5upTIl NXphn948EU/modYcyyXtI4svWfgQuSjl2ZSk//078M0DNffqzhrifYdgFl5TPum1/6 i5RVeXtSXlr2nVjqMIdeYg0RdGFI/x55eIgocqnM= Message-ID: <2ebfdf08-8752-431d-82e4-9567ec71d38c@arm.com> Date: Fri, 17 Apr 2026 17:07:49 +0100 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 next] arm_mpam: Fix MBA alloc_capable handling To: Ben Horgan , Zeng Heng , gshan@redhat.com, reinette.chatre@intel.com, fenghuay@nvidia.com, jonathan.cameron@huawei.com, tan.shaopeng@jp.fujitsu.com Cc: linux-kernel@vger.kernel.org, jic23@kernel.org, wangkefeng.wang@huawei.com References: <20260413090041.1174485-1-zengheng4@huawei.com> <8c47b769-dd97-4e52-8c9e-496156850a3d@arm.com> Content-Language: en-GB From: James Morse In-Reply-To: <8c47b769-dd97-4e52-8c9e-496156850a3d@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Zeng, Ben, On 17/04/2026 10:52, Ben Horgan wrote: > On 4/13/26 10:00, Zeng Heng wrote: >> The resctrl_arch_set_cdp_enabled() is never invoked with RDT_RESOURCE_MBA >> as the rid parameter. Consequently, >> mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled always remains false, >> making it unreliable for conditional checks. >> >> The original logic uses this field to determine MBA state, causing a bug >> where MBA allocation is permanently disabled after the mount with CDP >> option. Remounting without CDP cannot restore the MBA partition capability. > > Ah, I see. Thanks for spotting this and sending a patch. This shape of bug is likely - I've not had access to a platform with bandwidth monitors! >> Fix by using the cdp_enabled global parameter directly. Enable MBA >> partition only when CDP is disabled and the MBA resource class is >> present. Disable MBA partition otherwise. >> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c >> index a9938006d0e6..161fb8905e28 100644 >> --- a/drivers/resctrl/mpam_resctrl.c >> +++ b/drivers/resctrl/mpam_resctrl.c >> @@ -217,12 +217,10 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable) >> l3->mon.num_rmid = resctrl_arch_system_num_rmid_idx(); >> >> /* The mbw_max feature can't hide cdp as it's a per-partid maximum. */ >> - if (cdp_enabled && !mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled) >> - mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = false; >> - >> - if (mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled && >> - mpam_resctrl_controls[RDT_RESOURCE_MBA].class) >> + if (!cdp_enabled && mpam_resctrl_controls[RDT_RESOURCE_MBA].class) >> mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; >> + else >> + mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = false; My reading of the original: | if (mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled && | mpam_resctrl_controls[RDT_RESOURCE_MBA].class) | mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; is that it was trying to do this reset - but never running. (as Zeng's commit message describes). I've spoken to Ben - and the intent here is a bit more complicated... if resctrl does start calling: | resctrl_arch_set_cdp_enabled(RDT_RESOURCE_MBA, true) then we expect to receive two configurations, one for code and one for data, so the aliasing controls problem goes away. The above original code is re-enabling MBA in this case. It needs to ignore the global 'cdp_enabled' to be immune to the order of resctrl_arch_set_cdp_enabled() calls. While this might seem odd, as resctrl doesn't do this today - it is a valid enum value, and this is in the woolly "are we Xeon shaped" area. I think long term we need a list of non-aliasing controls (min and max etc) which need disabling when CDP enabled. But re-enabling them when called explicitly makes sense as we have to handle those enum value anyway. > Isn't it more that the existing checks are correct (if not totally necessary) and guard against > resctrl_arch_set_cdp_enabled() being called with RDT_RESOURCE_MBA but that re-enable on unmount is missing? > Does just adding this check make sense? As already commented in the function we assume that > resctrl_arch_set_cdp_enabled() is only called with enable=false on error or unmount. > > --- a/drivers/resctrl/mpam_resctrl.c > +++ b/drivers/resctrl/mpam_resctrl.c > @@ -224,6 +224,9 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable) > mpam_resctrl_controls[RDT_RESOURCE_MBA].class) > mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; > > + if (!cdp_enabled && mpam_resctrl_controls[RDT_RESOURCE_MBA].class) > + mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; > + > if (enable) { > if (mpam_partid_max < 1) > return -EINVAL; I'll add a comment above the original code quoted above describing what it does, and take your hunk here, (with a comment that its for umount): -------------%<------------- arm_mpam: resctrl: Fix MBA CDP alloc_capable handling on unmount The code to set MBA's alloc_capable to true appears to be trying to restore alloc_capable on unmount. This can never work because resctrl_arch_set_cdp_enabled() is never invoked with RDT_RESOURCE_MBA as the rid parameter. Consequently, mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled always remains false. The alloc_capable setting in resctrl_arch_set_cdp_enabled() is to re-enable MBA if the caller opts in to separate control values using CDP for this resource. This doesn't happen today. Add a comment to describe this. However a bug remains where MBA allocation is permanently disabled after the mount with CDP option. Remounting without CDP cannot restore the MBA partition capability. Add a check to re-enable MBA when CDP is disabled, which happens on unmount. --- @@ -220,10 +220,18 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable) if (cdp_enabled && !mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled) mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = false; + /* + * if resctrl has attempted to enable CDP on MBA, re-enable MBA as two + * configurations will provided so there is no aliasing problem. + */ if (mpam_resctrl_controls[RDT_RESOURCE_MBA].cdp_enabled && mpam_resctrl_controls[RDT_RESOURCE_MBA].class) mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; + /* On unmount when CDP is disabled, re-enable MBA */ + if (!cdp_enabled && mpam_resctrl_controls[RDT_RESOURCE_MBA].class) + mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true; + if (enable) { if (mpam_partid_max < 1) return -EINVAL; -------------%<------------- Ben - do you want a Co-developed by for this? While I'm at it: Reviewed-by: James Morse Thanks, James