On 16.06.21 11:52, Jan Beulich wrote: > On 16.06.2021 09:30, Juergen Gross wrote: >> Xen PV guests are specifying the highest used PFN via the max_pfn >> field in shared_info. This value is used by the Xen tools when saving >> or migrating the guest. >> >> Unfortunately this field is misnamed, as in reality it is specifying >> the number of pages (including any memory holes) of the guest, so it >> is the highest used PFN + 1. Renaming isn't possible, as this is a >> public Xen hypervisor interface which needs to be kept stable. >> >> The kernel will set the value correctly initially at boot time, but >> when adding more pages (e.g. due to memory hotplug or ballooning) a >> real PFN number is stored in max_pfn. This is done when expanding the >> p2m array, and the PFN stored there is even possibly wrong, as it >> should be the last possible PFN of the just added P2M frame, and not >> one which led to the P2M expansion. >> >> Fix that by setting shared_info->max_pfn to the last possible PFN + 1. >> >> Fixes: 98dd166ea3a3c3 ("x86/xen/p2m: hint at the last populated P2M entry") >> Cc: stable@vger.kernel.org >> Signed-off-by: Juergen Gross > > The code change is fine, so > Reviewed-by: Jan Beulich > > But I think even before the rename you would want to clarify the comment > next to the variable's definition, to make clear what it really holds. It already says: "Number of valid entries in the p2m table(s) ..." What do you think is unclear about that? Or do you mean another variable? Juergen