[Pkg-xen-devel] Bug#994870: Bug#994870: Memory allocation problem for VM after xen security update

[Hans van Kranenburg]

Hi Ruediger,

On 9/22/21 11:37 AM, H.-R. Oberhage wrote:
> Package: xen-system-amd64
> Version: 4.14.3-1~deb11u1
> 
> After applying the buster security update to xen, my VM won't start
> any longer, complaining about a memory allocation error.

Can you confirm that this is a virtual machine that tries to boot a
32-bit kernel as PV type?

The error message you are seeing is not particularly helpful, but it is
most likely related to this.

The fact that with this package update 32-bit PV guests fail to start is
indeed a regression problem, which is quite inconvenient for you, right now.

At this point I would really recommend to not wait for a fix to arrive
which makes it start again, but change your VM to use a 64-bit kernel.

Let me know if you need help or run into problems while making this change.

Running 32-bit PV at all is already 'on life support' upstream for quite
a while now, and it also not under security support any more.

In the long run, I'd suggest working towards having 64-bit guests in PVH
mode, since that's one of the best options we have these days.

If there's a reason you really cannot switch to a 64-bit kernel or move
the functionality of this virtual machine to a new fully 64 bit system,
switching the virtualization type from PV to HVM would also be an option.

> Switching back to the previous version 4.14.2+25-gb6a8c4f72d-2 lets
> the VM start (again,) normally.
> 
> /var/log/libvirt/libxl/libxl-driver.log:
> 2021-09-21 14:01:44.645+0000: xc: panic: xc_dom_boot.c:120: 
> xc_dom_boot_mem_init: can't allocate low memory for domain: Out of 
> memory
> 2021-09-21 14:01:44.653+0000: libxl: libxl_dom.c:593:libxl__build_dom: 
> xc_dom_boot_mem_init failed: Die Operation wird nicht unterstützt 
> [means: the operation is not supported]
> 2021-09-21 14:01:44.662+0000: libxl: 
> libxl_create.c:1576:domcreate_rebuild_done: Domain 1:cannot (re-)build 
> domain: -3
> 
> The error is triggered, regardless if there was a boot-parameter
> "dom0_mem=1024M:max=2048M" set or not.
> /etc/xen/xl.conf was unaltered, i.e. 'autoballoon' was implicitely set
> to "auto".
> 
> I am "on" Buster, kernel 5.10.0-8-amd64 (5.10.46-4), all relevant fixes
> included.

Apologies for the inconvenience,

Hans