linux-kernel - Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to balloon pages

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: <20120815100108.GA1999@redhat.com>
Date:	Wed, 15 Aug 2012 13:01:08 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Rafael Aquini <aquini@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to
 balloon pages

On Wed, Aug 15, 2012 at 10:48:39AM +0100, Mel Gorman wrote:
> On Wed, Aug 15, 2012 at 12:25:28PM +0300, Michael S. Tsirkin wrote:
> > On Wed, Aug 15, 2012 at 10:05:28AM +0100, Mel Gorman wrote:
> > > On Tue, Aug 14, 2012 at 05:11:13PM -0300, Rafael Aquini wrote:
> > > > On Tue, Aug 14, 2012 at 10:51:39PM +0300, Michael S. Tsirkin wrote:
> > > > > What I think you should do is use rcu for access.
> > > > > And here sync rcu before freeing.
> > > > > Maybe an overkill but at least a documented synchronization
> > > > > primitive, and it is very light weight.
> > > > > 
> > > > 
> > > > I liked your suggestion on barriers, as well.
> > > > 
> > > 
> > > I have not thought about this as deeply as I shouold but is simply rechecking
> > > the mapping under the pages_lock to make sure the page is still a balloon
> > > page an option? i.e. use pages_lock to stabilise page->mapping.
> > 
> > To clarify, are you concerned about cost of rcu_read_lock
> > for non balloon pages?
> > 
> 
> Not as such, but given the choice between introducing RCU locking and
> rechecking page->mapping under a spinlock I would choose the latter as it
> is more straight-forward.

OK but checking it how? page->mapping == balloon_mapping does not scale to
multiple balloons, so I hoped we can switch to
page->mapping->flags & BALLOON_MAPPING or some such,
but this means we dereference it outside the lock ...

We will also need to add some API to set/clear mapping so that driver
does not need to poke in mm internals, but that's easy.

> -- 
> Mel Gorman
> SUSE Labs
--
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/