On 05/04/18 15:42, George Dunlap wrote: > On Thu, Apr 5, 2018 at 2:06 PM, Juergen Gross <jgross@xxxxxxxx> wrote: >> On 05/04/18 15:00, Boris Ostrovsky wrote: >>> On 04/05/2018 08:19 AM, Juergen Gross wrote: >>>> On 05/04/18 12:06, George Dunlap wrote: >>>> >>>>> Aren't there flags in the binary somewhere that could tell the >>>>> toolstack / Xen whether the kernel in question needs the RSDP table in >>>>> lowmem, or whether it can be put higher? >>>> Not really. Analyzing the binary whether it accesses the rsdp_addr in >>>> the start_info isn't the way to go, IMO. >>>> >>>> I've sent a patch to xen-devel adding a quirk flag to the domain's >>>> config to enable the admin special casing such an "old" kernel. >>> >>> Can we backport latest struct hvm_start_info changes (which bumped >>> interface version) to 4.11 and pass RSDP only for versions >=1? >> >> And this would help how? >> >> RSDP address is passed today, the kernel just doesn't read it. And >> how should Xen know which interface version the kernel is supporting? >> And Xen needs to know that in advance in order to place the RSDP in >> low memory in case the kernel isn't reading the RSDP address from >> start_info. > > But the kernel image has ELF notes, right? You can put one that > indicates that this binary *does* know how to read the RSDP from the > start_info, and if you don't find that, put it in lowmem. Sow you would hurt BSD which does read the RSDP address correctly but (today) has no such ELF note. I think extending the PVH interface in such a way is no good idea. Juergen