linux-kernel - Re: [PATCH][RFC] x86, hotplug: Use zero page for monitor when resuming from hibernation

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]

Date:	Mon, 6 Jun 2016 13:34:14 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Chen, Yu C" <yu.c.chen@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>,
	"Brown, Len" <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
	Zhu Guihua <zhugh.fnst@...fujitsu.com>,
	Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH][RFC] x86, hotplug: Use zero page for monitor when
 resuming from hibernation

On Mon, Jun 6, 2016 at 12:40 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jun 06, 2016 at 03:59:06PM +0000, Chen, Yu C wrote:
>
>> > > + if (hibernation_in_resume())
>> > > +         mwait_ptr = empty_zero_page;
>> > > + else
>> > > +         mwait_ptr = &current_thread_info()->flags;
>> >
>> > Why is this conditional? Is there any case in which the zero page is not also
>> > correct?
>> I'm thinking of avoid unnecessary wakeup for normal CPU offline,  for example,
>> if one  driver uses  the zero page and access it.
>
> Writing to the zero page would be a major fail.

I would think the safest thing to do during resume from hibernation is
to use hlt instead of mwait, so there is no dependency on any memory
address.  It doesn't need the power management features of mwait
either because the CPU will be reset soon after the restored kernel
resumes.

--
Brian Gerst