Message-ID: <f061c60c-91f6-4d6b-83dd-36c7d2f92062@redhat.com>
Date: Tue, 15 Oct 2024 10:56:34 +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 10:53, David Hildenbrand wrote:
> On 15.10.24 10:41, David Hildenbrand wrote:
>> 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 A right, I remember that there was some outdated documentation.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.
>>
> 
> I think we can do some follow up cleanups, assuming is_kdump_kernel() here is correct:
> 
> diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
> index cca1827d3d2e..fbc5de66d03b 100644
> --- a/arch/s390/kernel/crash_dump.c
> +++ b/arch/s390/kernel/crash_dump.c
> @@ -609,7 +609,7 @@ int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
>           u64 hdr_off;
>    
>           /* If we are not in kdump or zfcp/nvme dump mode return */
> -       if (!oldmem_data.start && !is_ipl_type_dump())
> +       if (!dump_available())
>                   return 0;
>           /* If we cannot get HSA size for zfcp/nvme dump return error */
>           if (is_ipl_type_dump() && !sclp.hsa_size)
> diff --git a/arch/s390/kernel/os_info.c b/arch/s390/kernel/os_info.c
> index b695f980bbde..09578f400ef7 100644
> --- a/arch/s390/kernel/os_info.c
> +++ b/arch/s390/kernel/os_info.c
> @@ -148,7 +148,7 @@ static void os_info_old_init(void)
>    
>           if (os_info_init)
>                   return;
> -       if (!oldmem_data.start && !is_ipl_type_dump())
> +       if (!dump_available())
>                   goto fail;
>           if (copy_oldmem_kernel(&addr, __LC_OS_INFO, sizeof(addr)))
>                   goto fail;
> diff --git a/drivers/s390/char/zcore.c b/drivers/s390/char/zcore.c
> index 33cebb91b933..6a194b4f6ba5 100644
> --- a/drivers/s390/char/zcore.c
> +++ b/drivers/s390/char/zcore.c
> @@ -300,9 +300,7 @@ static int __init zcore_init(void)
>           unsigned char arch;
>           int rc;
>    
> -       if (!is_ipl_type_dump())
> -               return -ENODATA;
> -       if (oldmem_data.start)
> +       if (is_kdump_kernel())
>                   return -ENODATA;
>    
>           zcore_dbf = debug_register("zcore", 4, 1, 4 * sizeof(long));
> 
> 

Ugh, ignore the last one, I'm just confused about dumping options on 
s390x at this point :)

-- 
Cheers,

David / dhildenb

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