linux-kernel - Re: [PATCH v1 28/31] x86/resctrl: Drop __init/_

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Message-ID: <ZhfzF8L6w1pgJJ1r@e133380.arm.com>
Date: Thu, 11 Apr 2024 15:26:31 +0100
From: Dave Martin <Dave.Martin@....com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: James Morse <james.morse@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	carl@...amperecomputing.com, lcherian@...vell.com,
	bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
	dfustini@...libre.com, amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>
Subject: Re: [PATCH v1 28/31] x86/resctrl: Drop __init/__exit on assorted
 symbols

On Mon, Apr 08, 2024 at 08:32:36PM -0700, Reinette Chatre wrote:
> Hi James,
> 
> On 3/21/2024 9:51 AM, James Morse wrote:
> > Because ARM's MPAM controls are probed using MMIO, resctrl can't be
> > initialised until enough CPUs are online to have determined the
> > system-wide supported num_closid. Arm64 also supports 'late onlined
> > secondaries', where only a subset of CPUs are online during boot.
> > 
> > These two combine to mean the MPAM driver may not be able to initialise
> > resctrl until user-space has brought 'enough' CPUs online.
> > 
> > To allow MPAM to initialise resctrl after __init text has been free'd,
> > remove all the __init markings from resctrl.
> > 
> > The existing __exit markings cause these functions to be removed by the
> > linker as it has never been possible to build resctrl as a module. MPAM
> > has an error interrupt which causes the driver to reset and disable
> > itself. Remove the __exit markings to allow the MPAM driver to tear down
> > resctrl when an error occurs.
> 
> Obviously for the reasons you state this code has never been exercised.
> Were you able to test this error interrupt flow yet?
> 
> Reinette
> 

I think this will have to wait for James to respond.

There is code to tear down resctrl in response to an MPAM error interrupt,
but I don't know how it has been exercised so far (if at all).

https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/tree/drivers/platform/mpam/mpam_devices.c?h=mpam/snapshot/v6.7-rc2#n1940


Cheers
---Dave