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

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Message-ID: <0c7e876f-5648-4a82-b809-ca48f778b4a6@redhat.com>
Date: Tue, 15 Oct 2024 10:41:21 +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 15.10.24 10:30, Heiko Carstens wrote:
> On Mon, Oct 14, 2024 at 09:26:03PM +0200, David Hildenbrand wrote:
>> On 14.10.24 20:20, Heiko Carstens wrote:
>>> 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 A right, I remember that there was some outdated documentation.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
> 
> To be consistent with the rest of the comment, please write kdump in
> all lower case characters, please.

It obviously was too late in the evening for me :) Thanks!

> 
>> + * does no longer exist: setup_arch explicitly deactivates the elfcorehdr=
>> + * kernel parameter. The is_kudmp_kernel() implementation on s390 is independent
> 
> Typo: kudmp.
> 
>> 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" ?
> 
> Yes, it is some sort of kdump, even though a bit odd.

My concern is that we'll now have

bool is_kdump_kernel(void)
{
        return oldmem_data.start && !is_ipl_type_dump();
}

Which matches 3), but if 2) is also called "kdump", then should it 
actually be

bool is_kdump_kernel(void)
{
        return oldmem_data.start;
}

?

When I wrote that code I was rather convinced that the variant in this 
patch is the right thing to do.

-- 
Cheers,

David / dhildenb