linux-kernel - Re: [PATCH v1 3/6] x86/resctrl: Disallow mongroup rename on MPAM

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Date: Fri, 5 Apr 2024 15:10:07 -0700
From: Peter Newman <peternewman@...gle.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>, James Morse <james.morse@....com>, 
	Stephane Eranian <eranian@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>, 
	Uros Bizjak <ubizjak@...il.com>, Mike Rapoport <rppt@...nel.org>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Xin Li <xin3.li@...el.com>, 
	Babu Moger <babu.moger@....com>, Shaopeng Tan <tan.shaopeng@...itsu.com>, 
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, Jens Axboe <axboe@...nel.dk>, 
	Christian Brauner <brauner@...nel.org>, Oleg Nesterov <oleg@...hat.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Tycho Andersen <tandersen@...flix.com>, 
	Nicholas Piggin <npiggin@...il.com>, Beau Belgrave <beaub@...ux.microsoft.com>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/6] x86/resctrl: Disallow mongroup rename on MPAM

Hi Reinette,

On Thu, Apr 4, 2024 at 4:11 PM Reinette Chatre
<reinette.chatre@...el.com> wrote:
>
> Hi Peter,
>
> On 3/25/2024 10:27 AM, Peter Newman wrote:
> > Moving a monitoring group to a different parent control assumes that the
> > monitors will not be impacted. This is not the case on MPAM where the
> > PMG is an extension of the PARTID.
> >
> > Detect this situation by requiring the change in CLOSID not to affect
> > the result of resctrl_arch_rmid_idx_encode(), otherwise return
> > -EOPNOTSUPP.
> >
>
> Thanks for catching this. This seems out of place in this series. It sounds
> more like an independent fix that should go in separately.

I asserted in a comment in a patch later in the series that the
mongroup parent pointer never changes on MPAM, then decided to follow
up on whether it was actually true, so it's only here because this
series depends on it. I'll post it again separately with the fix you
requested below.

Thanks!
-Peter