Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

Baoquan He
2024-11-20T10:14:15Z

On 10/25/24 at 05:11pm, David Hildenbrand wrote:
> s390 allocates+prepares the elfcore hdr in the dump (2nd) kernel, not in
> the crashed kernel.
>
> RAM provided by memory devices such as virtio-mem can only be detected
> using the device driver; when vmcore_init() is called, these device
> drivers are usually not loaded yet, or the devices did not get probed
> yet. Consequently, on s390 these RAM ranges will not be included in
> the crash dump, which makes the dump partially corrupt and is
> unfortunate.
>
> Instead of deferring the vmcore_init() call, to an (unclear?) later point,
> let's reuse the vmcore_cb infrastructure to obtain device RAM ranges as
> the device drivers probe the device and get access to this information.
>
> Then, we'll add these ranges to the vmcore, adding more PT_LOAD
> entries and updating the offsets+vmcore size.
>
> Use Kconfig tricks to include this code automatically only if (a) there is
> a device driver compiled that implements the callback
> (PROVIDE_PROC_VMCORE_DEVICE_RAM) and; (b) the architecture actually needs
> this information (NEED_PROC_VMCORE_DEVICE_RAM).
>
> The current target use case is s390, which only creates an elf64
> elfcore, so focusing on elf64 is sufficient.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> fs/proc/Kconfig | 25 ++++++
> fs/proc/vmcore.c | 156 +++++++++++++++++++++++++++++++++++++
> include/linux/crash_dump.h | 9 +++
> 3 files changed, 190 insertions(+)
>
> diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> index d80a1431ef7b..1e11de5f9380 100644
> --- a/fs/proc/Kconfig
> +++ b/fs/proc/Kconfig
> @@ -61,6 +61,31 @@ config PROC_VMCORE_DEVICE_DUMP
> as ELF notes to /proc/vmcore. You can still disable device
> dump using the kernel command line option 'novmcoredd'.
>
> +config PROVIDE_PROC_VMCORE_DEVICE_RAM
> + def_bool n
> +
> +config NEED_PROC_VMCORE_DEVICE_RAM
> + def_bool n
> +
> +config PROC_VMCORE_DEVICE_RAM
> + def_bool y
> + depends on PROC_VMCORE
> + depends on NEED_PROC_VMCORE_DEVICE_RAM
> + depends on PROVIDE_PROC_VMCORE_DEVICE_RAM

Kconfig item is always a thing I need learn to master. When I checked
this part, I have to write them down to deliberate. I am wondering if
below 'simple version' works too and more understandable. Please help
point out what I have missed.

===========simple version======
config PROC_VMCORE_DEVICE_RAM
def_bool y
depends on PROC_VMCORE && VIRTIO_MEM
depends on NEED_PROC_VMCORE_DEVICE_RAM

config S390
select NEED_PROC_VMCORE_DEVICE_RAM
============

======= config items extracted from this patchset====
config PROVIDE_PROC_VMCORE_DEVICE_RAM
def_bool n

config NEED_PROC_VMCORE_DEVICE_RAM
def_bool n

config PROC_VMCORE_DEVICE_RAM
def_bool y
depends on PROC_VMCORE
depends on NEED_PROC_VMCORE_DEVICE_RAM
depends on PROVIDE_PROC_VMCORE_DEVICE_RAM

config VIRTIO_MEM
depends on X86_64 || ARM64 || RISCV
~~~~~ I don't get why VIRTIO_MEM dones't depend on S390 if
s390 need PROC_VMCORE_DEVICE_RAM.
......
select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE

config S390
select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
=================================================