Re: [Xen-devel] [PATCH] xen: convert p2m to a 3 level tree - partial revert

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Mon, 31 Jan 2011, Daniel Kiper wrote:
> Hi,
> 
> On Thu, Jan 27, 2011 at 10:25:08AM -0500, Konrad Rzeszutek Wilk wrote:
> > On Thu, Jan 27, 2011 at 03:48:43PM +0100, Daniel Kiper wrote:
> > > Hi,
> > >
> > > Durning work on Xen memory hotplug I discoverd that
> > > 2.6.38-rc2 does not boot on domU. After some investigation
> > > it appeared that 58e05027b530ff081ecea68e38de8d59db8f87e0
> > > commit changed CONFIG_XEN_MAX_DOMAIN_MEMORY constant value
> > > to 128. This change does not allow to boot kernel on domU
> > > with small memory size (I could confirm that it is even
> > > not possible to boot kernel on domU with 2 GiB). Guest
> >
> > Strange.. I've been booting with 1G, 2G, 3G, 4G guests.
> >
> > Could you give more details? Is this a 32-bit guest? 64-bit?
> > What does your xm file look like?
> >
> > > crash silently without any warning. Durning further
> > > research I found out that there is another commit published
> > > recently (8e1b4cf2108488ccfb9a3e7ed7cd85a435e01d4b) which attempts
> > > to fix this issue, however, it does not work on my platform.
> > > I decided to reenable CONFIG_XEN_MAX_DOMAIN_MEMORY option in
> > > kernel config and enable users to choose resonable values for
> > > their machines until better fix will be published. I think this
> > > solution is good because allow users to boot domU with newest
> > > kernel and allow developers to continue their work without
> > > time presure which could lead to new bugs.
> >
> > I think you are hitting a completly different bug. This
> > patch of yours changes the size of the structure - so it could
> > be that you are hitting a page-table overwrite. This is something
> > that Stefano has been looking at - you might want to take a look at
> > "x86: When destroying mappings between _brk_end and _end, do not go over _end"
> > (it is present in his git tree).
> 
> It appears that this patch fixed issue described above. In this
> situation I think it should be applied ASAP to RC and stable kernels.
> 

I am reworking the patch as we speak, I should have an upstreamable
version ready very soon.