Re: [PATCH v2 00/12] fs/proc/vmcore: kdump support for virtio-mem on s390

Heiko Carstens
2025-01-08T12:10:55Z

On Wed, Jan 08, 2025 at 07:04:23AM -0500, Michael S. Tsirkin wrote:
> On Wed, Dec 04, 2024 at 01:54:31PM +0100, David Hildenbrand wrote:
> > 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
> > kdump kernel must detect memory ranges of the crashed 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
> > 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().
> >
> > To add these device RAM ranges to the vmcore ("patch the vmcore"), we will
> > add new PT_LOAD entries that describe these memory ranges, and update
> > all offsets vmcore size so it is all consistent.
> >
> > My testing when creating+analyzing crash dumps with hotplugged virtio-mem
> > memory (incl. holes) did not reveal any surprises.
> >
> > Patch #1 -- #7 are vmcore preparations and cleanups
> > Patch #8 adds the infrastructure for drivers to report device RAM
> > Patch #9 + #10 are virtio-mem preparations
> > Patch #11 implements virtio-mem support to report device RAM
> > Patch #12 activates it for s390, implementing a new function to fill
> > PT_LOAD entry for device RAM
>
> Who is merging this?
> virtio parts:
>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>

I guess this series should go via Andrew Morton. Andrew?

Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390