linux-kernel - Re: [PATCH v2 1/7] s390/kdump: implement is_kdump

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Message-ID: <f93b2c89-821a-4da1-8953-73ccd129a074@redhat.com>
Date: Mon, 14 Oct 2024 21:26:03 +0200
From: David Hildenbrand <david@...hat.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Cornelia Huck <cohuck@...hat.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...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>, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Mario Casquero <mcasquer@...hat.com>
Subject: Re: [PATCH v2 1/7] s390/kdump: implement is_kdump_kernel()

On 14.10.24 20:20, Heiko Carstens wrote:
> On Mon, Oct 14, 2024 at 04:46:13PM +0200, David Hildenbrand wrote:
>> s390 currently always results in is_kdump_kernel() == false, because
>> it sets "elfcorehdr_addr = ELFCORE_ADDR_MAX;" early during setup_arch to
>> deactivate the elfcorehdr= kernel parameter.
>>
>> Let's follow the powerpc example and implement our own logic.
>>
>> This is required for virtio-mem to reliably identify a kdump
>> environment to not try hotplugging memory.
>>
>> Tested-by: Mario Casquero <mcasquer@...hat.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>   arch/s390/include/asm/kexec.h | 4 ++++
>>   arch/s390/kernel/crash_dump.c | 6 ++++++
>>   2 files changed, 10 insertions(+)
> 
> Looks like this could work. But the comment in smp.c above
> dump_available() needs to be updated.

A right, I remember that there was some outdated documentation.

> 
> Are you willing to do that, or should I provide an addon patch?
> 

I can squash the following:

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 4df56fdb2488..a4f538876462 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -587,16 +587,16 @@ int smp_store_status(int cpu)
   *    with sigp stop-and-store-status. The firmware or the boot-loader
   *    stored the registers of the boot CPU in the absolute lowcore in the
   *    memory of the old system.
- * 3) kdump and the old kernel did not store the CPU state,
- *    or stand-alone kdump for DASD
- *    condition: OLDMEM_BASE != NULL && !is_kdump_kernel()
+ * 3) kdump or stand-alone kdump for DASD
+ *    condition: OLDMEM_BASE != NULL && !is_ipl_type_dump() == false
   *    The state for all CPUs except the boot CPU needs to be collected
   *    with sigp stop-and-store-status. The kexec code or the boot-loader
   *    stored the registers of the boot CPU in the memory of the old system.
- * 4) kdump and the old kernel stored the CPU state
- *    condition: OLDMEM_BASE != NULL && is_kdump_kernel()
- *    This case does not exist for s390 anymore, setup_arch explicitly
- *    deactivates the elfcorehdr= kernel parameter
+ *
+ * Note that the old Kdump mode where the old kernel stored the CPU state
+ * does no longer exist: setup_arch explicitly deactivates the elfcorehdr=
+ * kernel parameter. The is_kudmp_kernel() implementation on s390 is independent
+ * of the elfcorehdr= parameter.
   */
  static bool dump_available(void)
  {

Does that sound reasonable? I'm not so sure about the "2) stand-alone kdump for
SCSI/NVMe (zfcp/nvme dump with swapped memory)": is that really "kdump" ?

-- 
Cheers,

David / dhildenb