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.
Thanks!
--
Cheers,
David / dhildenb
