Re: [PATCH] KVM: Veirfy memory slot only for readability

[Avi Kivity <avi@redhat.com>]

On 12/04/2011 07:29 PM, Sasha Levin wrote:
> On Sun, 2011-12-04 at 18:53 +0200, Avi Kivity wrote:
> > On 12/02/2011 07:46 AM, Sasha Levin wrote:
> > > > Do you want to create read only memory slots for kvm tool?
> > >
> > > What KVM tool currently does is copy the kernel into guest memory and
> > > run it from there. An idea raised recently was instead of copying it we
> > > should mmap it into the memory to reduce footprint.
> > >
> > > This is why I'm looking into adding a read only memory slot. The KVM
> > > code doesn't have to know it's read only.
> > 
> > The kernel will patch itself very early.  You need to use MAP_PRIVATE
> > (and thus have a read/write area).  It will be interesting to see what
> > fraction of the memory is modified.
> > 
> > Note that mapping will remove benefits like huge page support, and that
> > you can get page sharing by using ksm.  Still, it's interesting to see
> > where this goes.
>
> Why would I lose hugepage if the kernel gets it's own memory slot?

(transparent) hugepages only work on anonymous memory.  Hopefully later
it will be extended to work on mapped memory as well.

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