linux-kernel - Re: [PATCH] x86/resctrl: Do not round up mba

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <623a4a0d-b479-4bfe-9c2b-b62584a19738@intel.com>
Date: Fri, 27 Sep 2024 15:46:46 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
	"Maciej Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>, Borislav Petkov <bp@...en8.de>, Martin Kletzander
	<nert.pinx@...il.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH] x86/resctrl: Do not round up mba_MBps values in schemata
 file

+Martin

Hi Tony,

On 9/27/24 3:30 PM, Tony Luck wrote:
> When the mba_MBps mount option is used Linux initializes the
> MBA control values in the schemata file to MBA_MAX_MBPS (which
> is defined as U32_MAX). So the schemata file contains this line:
> 
>  MB:0=4294967295;1=4294967295
> 
> If a user edits the schemata file with vi(1) (or other editor) and
> simply writes that line back, it gets changed to:
> 
>   MB:0=   4;1=   4
> 
> which sets maximum bandwidth to a very low value.
> 
> This happens because bw_validate() unconditionally rounds user supplied
> values up to next multiple of r->membw.bw_gran. That results in a value
> that will not fit into d->mbps_val[closid].
> 
> Rounding up only makes sense when mba_MBps is not enabled and control
> values are expressed as percentage values.
> 
> Skip the roundup() when mba_MBps is enabled.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---

A fix for this issue is already being discussed. Please see latest fix
at [1] that additionally addresses the issue if a user attempts to 
write a value larger than 4294967295. Could you please check if that
fix works for you?

Thank you.

Reinette

[1] https://lore.kernel.org/all/a7c80676-0761-4618-ac07-0b53434b1a9b@intel.com/