linux-kernel - Re: [patch 2/4] mmu_notifier: Callbacks to invalidate address ranges

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:	Fri, 1 Feb 2008 18:21:45 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Robin Holt <holt@....com>, Andrea Arcangeli <andrea@...ranet.com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/4] mmu_notifier: Callbacks to invalidate address
	ranges

On Fri, Feb 01, 2008 at 04:05:08PM -0800, Christoph Lameter wrote:
> On Fri, 1 Feb 2008, Robin Holt wrote:
> 
> > On Fri, Feb 01, 2008 at 03:19:32PM -0800, Christoph Lameter wrote:
> > > On Fri, 1 Feb 2008, Robin Holt wrote:
> > > 
> > > > We are getting this callout when we transition the pte from a read-only
> > > > to read-write.  Jack and I can not see a reason we would need that
> > > > callout.  It is causing problems for xpmem in that a write fault goes
> > > > to get_user_pages which gets back to do_wp_page that does the callout.
> > > 
> > > Right. You placed it there in the first place. So we can drop the code 
> > > from do_wp_page?
> > 
> > No, we need a callout when we are becoming more restrictive, but not
> > when becoming more permissive.  I would have to guess that is the case
> > for any of these callouts.  It is for both GRU and XPMEM.  I would
> > expect the same is true for KVM, but would like a ruling from Andrea on
> > that.
> 
> do_wp_page is entered when the pte shows that the page is not writeable 
> and it makes the page writable in some situations. Then we do not 
> invalidate the remote reference.
> 
> However, when we do COW then a *new* page is put in place of the existing 
> readonly page. At that point we need to remove the remote pte that is 
> readonly. Then we install a new pte pointing to a *different* page that is 
> writable.
> 
> Are you saying that you get the callback when transitioning from a read 
> only to a read write pte on the *same* page?

I believe that is what we saw.  We have not put in any more debug
information yet.  I will try to squeze it in this weekend.  Otherwise,
I will probably have to wait until early Monday.

Thanks
Robin
--
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/