On Thu, May 15, 2025 at 11:01:24AM +0200, Marek Marczykowski-Górecki wrote:

On Wed, May 14, 2025 at 10:04:26AM +0200, Roger Pau Monne wrote:

...

When adding extra memory regions as ballooned pages also adjust the balloon target, otherwise when the balloon driver is started it will populate memory to match the target value and consume all the extra memory regions added.

This made the usage of the Xen `dom0_mem=,max:` command line parameter for dom0 not work as expected, as the target won't be adjusted and when the balloon is started it will populate memory straight to the 'max:' value. It would equally affect domUs that have memory != maxmem.

Kernels built with CONFIG_XEN_UNPOPULATED_ALLOC are not affected, because the extra memory regions are consumed by the unpopulated allocation driver, and then balloon_add_regions() becomes a no-op.

Reported-by: John jw@nuclearfallout.net Fixes: 87af633689ce ('x86/xen: fix balloon target initialization for PVH dom0') Signed-off-by: Roger Pau Monné roger.pau@citrix.com

Tested-by: Marek Marczykowski-Górecki marmarek@invisiblethingslab.com

I think this wants Cc: stable, since the commit named in Fixes: got backported too. Or is the Fixes tag enough?