From: Sourabh Jain <sourabhjain@linux.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>,
linuxppc-dev@ozlabs.org
Cc: Aditya Gupta <adityag@linux.ibm.com>,
Mahesh Salgaonkar <mahesh@linux.ibm.com>,
Hari Bathini <hbathini@linux.ibm.com>
Subject: Re: [PATCH v5 1/3] powerpc: make fadump resilient with memory add/remove events
Date: Fri, 24 Nov 2023 12:51:17 +0530 [thread overview]
Message-ID: <f75a2cd4-e75d-40d0-bf86-e3f8cc9ce302@linux.ibm.com> (raw)
In-Reply-To: <87cyw2j6h1.fsf@mail.lhotse>
Hello Michael,
On 22/11/23 18:22, Michael Ellerman wrote:
> Sourabh Jain <sourabhjain@linux.ibm.com> writes:
>> On 22/11/23 10:47, Michael Ellerman wrote:
>>> Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> writes:
>>> ...
>>>> I am not sure whether we need to add all the complexity to enable supporting different fadump kernel
>>>> version. Is that even a possible use case with fadump? Can't we always assume that with fadump the
>>>> crash kernel and fadump kernel will be same version?
>>> How sure are we of that?
>>>
>>> Don't we go through grub when we boot into the 2nd kernel. And so
>>> couldn't it choose to boot a different kernel, for whatever reason.
>>>
>>> I don't think we need to support different pt_reg / cpumask sizes, but
>>> requiring the exact same kernel version is too strict I think.
>> Agree.
>>> But maybe I'm wrong. Would be good to hear what distro folks think.
>> How about checking fadump crash info header compatibility in the
>> following way?
>>
>> static bool is_fadump_header_compatible(struct fadump_crash_info_header
>> *fdh)
>> {
>> if (fdh->magic_number == FADUMP_CRASH_INFO_MAGIC_OLD) {
>> pr_err("Old magic number, can't process the dump.");
>> return false;
>> }
>>
>> if (fdh->magic_number != FADUMP_CRASH_INFO_MAGIC) {
>> pr_err("Fadump header is corrupted.");
>> return false;
>> }
>>
>> /*
>> * If the kernel version of the first/crashed kernel and the
>> second/fadump
>> * kernel is not same, then only collect the dump if the size of all
>> * non-primitive type members of the fadump header is the same
>> across kernels.
>> */
>> if (strcmp(fdh->kernel_version, init_uts_ns.name.release)) {
>
> I don't think the kernel version check is necessary?
I didn't find a place where pt_regs members are accessed to take
a decision in fadump kernel. we just copy the pt_regs in fadump kernel.
So I think as long as size is same across kernels, we are good.
>
>> if (fdh->pt_regs_sz != sizeof(struct pt_regs) || fdh->cpu_mask_sz != sizeof(struct cpumask)) {
>> pr_err("Fadump header size mismatch.\n")
>> return false;
> Yeah I think that works.
>
>> } else
>> pr_warn("Kernel version mismatch; dump data is unreliable.\n");
>> }
>>
>> return true;
>> }
>>
>> And the new fadump crash info header will be: As suggested by Hari.
>>
>> /* fadump crash info structure */
>> struct fadump_crash_info_header {
>> u64 magic_number;
>> + u32 version;
>
> Do we need version? We're effectively using the magic_number as a
> version already. Having an actual version would allow us to make
> backward compatible changes in future, but it's not clear we'll need or
> want to do that.
Agree that currently version field is not used but I added a version
field to
make the fadump header structure compatible with future changes without
changing the magic number.
I will add a comment on how version field should be utilized if one
changes fadump
header in future.
>
>> u32 crashing_cpu;
>> u64 elfcorehdr_addr;
>> + u64 elfcorehdr_size;
>> + u64 vmcoreinfo_raddr;
>> + u64 vmcoreinfo_size;
>> + u8 kernel_version[__NEW_UTS_LEN + 1];
>> + u32 pt_regs_sz;
>> struct pt_regs regs;
>> + u32 cpu_mask_sz;
>
> Typically you would put all the size fields before the variable sized
> fields, because otherwise the later size fields may not be where you
> expect them to be. But because we're bailing out if any of the sizes
> don't match it doesn't actually matter.
Yeah, but I will reorganize fadump header and put the size fields before the
variable sized fields.
>
>> struct cpumask cpu_mask;
>> };
> The other issue is endian. I assume we're just declaring that the
> 1st/2nd kernel must be the same endian? We should still make that
> explicit though.
A comment is fine or should we add a explicit check and error out
with relevant error message if endianness is not same across the
kernels?
Something like:
if (fdh->magic_number != FADUMP_CRASH_INFO_MAGIC) {
if (fdh->magic_number == swab64(FADUMP_CRASH_INFO_MAGIC)) {
pr_err("Endianness mismatch");
} else {
pr_err("Fadump header is corrupted.");
}
return false;
}
>
> To make it clearer that this struct is somewhat an ABI, I think we
> should move the definition into arch/powerpc/include/uapi/asm/fadump.h
Sure
>
> We don't expect userspace to actually use the header, but it will
> hopefully remind everyone that the struct needs to be changed with care :)
Agree
Thanks,
Sourabh Jain
next prev parent reply other threads:[~2023-11-24 7:27 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-29 12:45 [PATCH v5 0/3] powerpc: make fadump resilient with memory add/remove events Sourabh Jain
2023-10-29 12:45 ` [PATCH v5 1/3] " Sourabh Jain
2023-11-09 12:14 ` Michael Ellerman
2023-11-13 6:42 ` Sourabh Jain
2023-11-15 4:44 ` Aneesh Kumar K.V
2023-11-17 4:33 ` Sourabh Jain
2023-11-17 5:31 ` Aneesh Kumar K V
2023-11-17 6:14 ` Hari Bathini
2023-11-22 5:17 ` Michael Ellerman
2023-11-22 10:35 ` Sourabh Jain
2023-11-22 12:20 ` Aneesh Kumar K V
2023-11-24 5:20 ` Sourabh Jain
2023-11-22 12:52 ` Michael Ellerman
2023-11-24 7:21 ` Sourabh Jain [this message]
2023-10-29 12:45 ` [PATCH v5 2/3] powerpc/fadump: add hotplug_ready sysfs interface Sourabh Jain
2023-10-29 12:45 ` [PATCH v5 3/3] Documentation/powerpc: update fadump implementation details Sourabh Jain
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