linux-kernel - Re: [PATCH 3/5] vhost: support upto 509 memory regions

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Date:	Wed, 17 Jun 2015 14:23:39 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	pbonzini@...hat.com
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions

On Wed, 17 Jun 2015 13:51:56 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Jun 17, 2015 at 01:48:03PM +0200, Igor Mammedov wrote:
> > > > So far it's kernel limitation and this patch fixes crashes
> > > > that users see now, with the rest of patches enabling performance
> > > > not to regress.
> > > 
> > > When I say regression I refer to an option to limit the array
> > > size again after userspace started using the larger size.
> > Is there a need to do so?
> 
> Considering userspace can be malicious, I guess yes.
I don't think it's a valid concern in this case,
setting limit back from 509 to 64 will not help here in any way,
userspace still can create as many vhost instances as it needs
to consume memory it desires.

> 
> > Userspace that cares about memory footprint won't use many slots
> > keeping it low and user space that can't do without many slots
> > or doesn't care will have bigger memory footprint.
> 
> We really can't trust userspace to do the right thing though.
> 

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