On 22.04.20 11:17, Baoquan He wrote: > On 04/21/20 at 03:29pm, David Hildenbrand wrote: >>>> ACPI SRAT is embeded into efi, need read out the rsdp pointer. If we don't >>>> pass the efi, it won't get the SRAT table correctly, if I remember >>>> correctly. Yeah, I remeber kvm guest can get memory hotplugged with >>>> ACPI only, this won't happen on bare metal though. Need check carefully. >>>> I have been using kvm guest with uefi firmwire recently. >>> >>> Yeah, I can imagine that bare metal is different. kvm only uses ACPI. >>> >>> I'm also asking because of virtio-mem. Memory added via virtio-mem is >>> not part of any efi tables or whatsoever. So I assume the kexec kernel >>> will not detect it automatically (good!), instead load the virtio-mem >>> driver and let it add memory back to the system. >>> >>> I should probably play with kexec and virtio-mem once I have some spare >>> cycles ... to find out what's broken and needs to be addressed :) >> >> FWIW, I just gave virtio-mem and kexec/kdump a try. >> >> a) kdump seems to work. Memory added by virtio-mem is getting dumped. >> The kexec kernel only uses memory in the crash region. The virtio-mem >> driver properly bails out due to is_kdump_kernel(). > > Right, kdump is not impacted later added memory. > >> >> b) "kexec -s -l" seems to work fine. For now, the kernel does not seem >> to get placed on virtio-mem memory (pure luck due to the left-to-right >> search). Memory added by virtio-mem is not getting added to the e820 >> map. Once the virtio-mem driver comes back up in the kexec kernel, the >> right memory is readded. > > kexec_file_load just behaves as you tested. It doesn't collect later > added memory to e820 because it uses e820_table_kexec directly to pass > e820 to kexec-ed kernel. However, this e820_table_kexec is only updated > during boot stage. I tried hot adding DIMM after boot, kexec-ed kernel > doesn't have it in e820 during bootup, but it's recoginized and added > when ACPI scanning. I think we should update e820_table_kexec when hot > add/remove memory, at least for DIMM. Not sure if DLPAR, virtio-mem, > balloon will need be added into e820_table_kexec too, and if this is > expected behaviour. > > But whatever we do, it won't impact the kexec file_loading, because of > the searching strategy bottom up. Just adding them into e820_table_kexec > will make it consistent with cold reboot which get recognizes and get > them into e820 during bootup. Yeah, I think whatever a cold-booted kernel will see is what kexec-ed kernel should see. Not more, not less. Regarding virtio-mem: Not in e820 on cold-boot. Regarding DIMMs: DIMMs under KVM will never show up in the e820 map IIRC. I think on real HW it can be different. -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
