linux-kernel - Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc

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, 25 Nov 2013 16:06:56 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Avi Kivity <avi.kivity@...il.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	"pbonzini@...hat.com Bonzini" <pbonzini@...hat.com>,
	linux-kernel@...r.kernel.org, kvm <kvm@...r.kernel.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc

GOn Mon, Nov 25, 2013 at 04:29:28PM +0200, Gleb Natapov wrote:
> On Mon, Nov 25, 2013 at 12:23:51PM -0200, Marcelo Tosatti wrote:
> > On Mon, Nov 25, 2013 at 02:48:37PM +0200, Avi Kivity wrote:
> > > On Mon, Nov 25, 2013 at 8:11 AM, Xiao Guangrong
> > > <xiaoguangrong@...ux.vnet.ibm.com> wrote:
> > > >
> > > > On Nov 23, 2013, at 3:14 AM, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> > > 
> > > <snip complicated stuff about parent_pte>
> > > 
> > > I'm not really following, but note that parent_pte predates EPT (and
> > > the use of rcu in kvm), so all the complexity that is the result of
> > > trying to pack as many list entries into a cache line can be dropped.
> > > Most setups now would have exactly one list entry, which is handled
> > > specially antyway.
> > > 
> > > Alternatively, the trick of storing multiple entries in one list entry
> > > can be moved to generic code, it may be useful to others.
> > 
> > Yes, can the lockless list walking code be transformed into generic
> > single-linked list walking? So the correctness can be verified
> > independently, and KVM becomes a simple user of that interface.
> > 
> The code will become simpler but the problem of never ending walk of
> rculist_nulls will remain.

Yes. Hopefully it can be fixed in some way.

> > The simpler version is to maintain lockless walk on depth-1 rmap entries
> > (and grab the lock once depth-2 entry is found).
> And release it between each rmap walk or at the very end of write
> protect?

Or keep it locked until 10 consecutive sptes with depth 1 are found.

--
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/