linux-kernel - Re: [PATCH 1/2] x86/intel_rdt: Check monitor group vs control group membership earlier

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Message-ID: <jhjv9e0uir6.mognet@arm.com>
Date:   Fri, 20 Nov 2020 15:53:49 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     James Morse <james.morse@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86/intel_rdt: Check monitor group vs control group membership earlier


Hi James,

On 20/11/20 14:53, James Morse wrote:
> Hi Valentin,
>
> On 18/11/2020 18:00, Valentin Schneider wrote:
>> A task can only be moved between monitor groups if both groups belong to
>> the same control group. This is checked fairly late however: by that time
>> we already have appended a task_work() callback.
>
> (is that a problem? It's needed to do the kfree())
>
>
>> Check the validity of the move before getting anywhere near task_work
>> callbacks.
>
> This saves the kzalloc()/task_work_add() if it wasn't going to be necessary.
>

Right, to hopefully better point it out:

In such cases (invalid move), __rdtgroup_move_task() would trigger a
move_myself() task_work callback without updating {closid, rmid}.
Given nothing changed (barring concurrent updates), move_myself() won't do
any useful work.

The task_work_add() and associated alloc could thus be entirely avoided.

> Reviewed-by: James Morse <james.morse@....com>
>

Thanks!

>
> Thanks,
>
> James