On 11/15/24 at 09:55am, David Hildenbrand wrote: > On 15.11.24 09:46, Baoquan He wrote: > > On 10/25/24 at 05:11pm, David Hildenbrand wrote: > > > This is based on "[PATCH v3 0/7] virtio-mem: s390 support" [1], which adds > > > virtio-mem support on s390. > > > > > > The only "different than everything else" thing about virtio-mem on s390 > > > is kdump: The crash (2nd) kernel allocates+prepares the elfcore hdr > > > during fs_init()->vmcore_init()->elfcorehdr_alloc(). Consequently, the > > > crash kernel must detect memory ranges of the crashed/panicked kernel to > > > include via PT_LOAD in the vmcore. > > > > > > On other architectures, all RAM regions (boot + hotplugged) can easily be > > > observed on the old (to crash) kernel (e.g., using /proc/iomem) to create > > > the elfcore hdr. > > > > > > On s390, information about "ordinary" memory (heh, "storage") can be > > > obtained by querying the hypervisor/ultravisor via SCLP/diag260, and > > > that information is stored early during boot in the "physmem" memblock > > > data structure. > > > > > > But virtio-mem memory is always detected by as device driver, which is > > > usually build as a module. So in the crash kernel, this memory can only be > > ~~~~~~~~~~~ > > Is it 1st kernel or 2nd kernel? > > Usually we call the 1st kernel as panicked kernel, crashed kernel, the > > 2nd kernel as kdump kernel. > > It should have been called "kdump (2nd) kernel" here indeed. > > > > properly detected once the virtio-mem driver started up. > > > > > > The virtio-mem driver already supports the "kdump mode", where it won't > > > hotplug any memory but instead queries the device to implement the > > > pfn_is_ram() callback, to avoid reading unplugged memory holes when reading > > > the vmcore. > > > > > > With this series, if the virtio-mem driver is included in the kdump > > > initrd -- which dracut already takes care of under Fedora/RHEL -- it will > > > now detect the device RAM ranges on s390 once it probes the devices, to add > > > them to the vmcore using the same callback mechanism we already have for > > > pfn_is_ram(). > > > > Do you mean on s390 virtio-mem memory region will be detected and added > > to vmcore in kdump kernel when virtio-mem driver is initialized? Not > > sure if I understand it correctly. > > Yes exactly. In the kdump kernel, the driver gets probed and registers the > vmcore callbacks. From there, we detect and add the device regions. I see now, thanks for your confirmation.
