linux-kernel - Re: [PATCH v1 00/11] fs/proc/vmcore: kdump support for virtio-mem on s390

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Message-ID: <Zyhn0oz+ze0xY2AR@MiWiFi-R3L-srv>
Date: Mon, 4 Nov 2024 14:21:06 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 00/11] fs/proc/vmcore: kdump support for virtio-mem on
 s390

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
> 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.
> 
> Note that makedumfile is shaky with v6.12-rcX, I made the "obvious" things
> (e.g., free page detection) work again while testing as documented in [2].
> 
> Creating the dumps using makedumpfile seems to work fine, and the
> dump regions (PT_LOAD) are as expected. I yet have to check in more detail
> if the created dumps are good (IOW, the right memory was dumped, but it
> looks like makedumpfile reads the right memory when interpreting the
> kernel data structures, which is promising).
> 
> Patch #1 -- #6 are vmcore preparations and cleanups

Thanks for CC-ing me, I will review the patch 1-6, vmcore part next
week.