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

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Message-ID: <9be496ff-9d94-4680-b095-863ec12e3261@redhat.com>
Date: Tue, 15 Oct 2024 10:53:37 +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 10:41, 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 A right, I remember that there was some outdated documentation.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));


-- 
Cheers,

David / dhildenb