On Tue, Jan 20, 2026 at 03:06:47PM +0100, Roger Pau Monne wrote: > This partially reverts commit 87af633689ce16ddb166c80f32b120e50b1295de so > the current memory target for PV guests is still fetched from > start_info->nr_pages, which matches exactly what the toolstack sets the > initial memory target to. > > Using get_num_physpages() is possible on PV also, but needs adjusting to > take into account the ISA hole and the PFN at 0 not considered usable > memory depite being populated, and hence would need extra adjustments. > Instead of carrying those extra adjustments switch back to the previous > code. That leaves Linux with a difference in how current memory target is > obtained for HVM vs PV, but that's better than adding extra logic just for > PV. > > Also, for HVM the target is not (and has never been) accurately calculated, > as in that case part of what starts as guest memory is reused by hvmloader > and possibly other firmware to store ACPI tables and similar firmware > information, thus the memory is no longer being reported as RAM in the > memory map. > > Reported-by: James Dingwall <[email protected]> > Signed-off-by: Roger Pau Monné <[email protected]> > --- > drivers/xen/balloon.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c > index 49c3f9926394..e799650f6c8c 100644 > --- a/drivers/xen/balloon.c > +++ b/drivers/xen/balloon.c > @@ -724,6 +724,7 @@ static int __init balloon_add_regions(void) > static int __init balloon_init(void) > { > struct task_struct *task; > + unsigned long current_pages; > int rc; > > if (!xen_domain()) > @@ -731,12 +732,15 @@ static int __init balloon_init(void) > > pr_info("Initialising balloon driver\n"); > > - if (xen_released_pages >= get_num_physpages()) { > + current_pages = xen_pv_domain() ? min(xen_start_info->nr_pages, max_pfn) > + : get_num_physpages(); > + > + if (xen_released_pages >= current_pages) { > WARN(1, "Released pages underflow current target"); > return -ERANGE; > } > > - balloon_stats.current_pages = get_num_physpages() - xen_released_pages; > + balloon_stats.current_pages = current_pages - xen_released_pages; > balloon_stats.target_pages = balloon_stats.current_pages; > balloon_stats.balloon_low = 0; > balloon_stats.balloon_high = 0; > -- > 2.51.0 >
Thank you Roger, I tested this patch on the system which originally showed the error and the pci passthrough now works as expected. Regards, James
