linux-kernel - Re: [PATCH 07/14] [POWERPC] Populate cpu_enabled

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: <20080716010418.GH10919@ldl.fc.hp.com>
Date:	Tue, 15 Jul 2008 19:04:18 -0600
From:	Alex Chiang <achiang@...com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-acpi@...r.kernel.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 07/14] [POWERPC] Populate cpu_enabled_map

* Benjamin Herrenschmidt <benh@...nel.crashing.org>:
> On Mon, 2008-07-14 at 20:34 -0600, Alex Chiang wrote:
> > Populate the cpu_enabled_map correctly.
> > 
> > Note that this patch does not actually make any decisions based
> > on the contents of the map.
> > 
> > However, as the map is presented via sysfs in:
> > 
> > 	/sys/devices/system/cpu/
> > 
> > It should be populated correctly.
> 
> Care to educate me on the difference between online_map and
> enabled_map ?

enabled_map is closer conceptually to present_map than
online_map.

present_map are CPUs that are actually plugged in

online_map are CPUs that have had cpu_up() called on them; ie.
schedulable

enabled_map is somewhere inbetween -- the CPUs are plugged in,
but we don't want to cpu_up() them. On hp ia64 systems, these
CPUs are disabled by system firmware.

Currently, a user can only configure/deconfigure the CPUs from
the system firmware interface. By providing a sysfs interface for
these CPUs, we can allow the user to configure/deconfigure them
from userspace. More realistically, higher level managability
software now has an OS-level interface to interact with these
CPUs.

Might this be useful for ppc and your hypervisor based
architecture? I could imagine your hypervisor telling the kernel
about all the physically present CPUs, but then you would be able
to have finer grained control using the enabled_map.

I haven't studied your code in depth, so maybe you can just do
everything with pure online/offline, but at least on my
platforms, there are use-cases where we might want something
in-between.

Thanks.

/ac

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/