linux-kernel - Re: [PATCH v3 10/12] ppc64/kexec_file: prepare elfcore header for crashing kernel

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Message-ID: <87a6zzcedg.fsf@morokweng.localdomain>
Date:   Thu, 16 Jul 2020 18:57:15 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Hari Bathini <hbathini@...ux.ibm.com>
Cc:     Pingfan Liu <piliu@...hat.com>, Nayna Jain <nayna@...ux.ibm.com>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 10/12] ppc64/kexec_file: prepare elfcore header for crashing kernel


Hari Bathini <hbathini@...ux.ibm.com> writes:

> On 16/07/20 7:52 am, Thiago Jung Bauermann wrote:
>> 
>> Hari Bathini <hbathini@...ux.ibm.com> writes:
>> 
>>>  /**
>>> + * get_crash_memory_ranges - Get crash memory ranges. This list includes
>>> + *                           first/crashing kernel's memory regions that
>>> + *                           would be exported via an elfcore.
>>> + * @mem_ranges:              Range list to add the memory ranges to.
>>> + *
>>> + * Returns 0 on success, negative errno on error.
>>> + */
>>> +static int get_crash_memory_ranges(struct crash_mem **mem_ranges)
>>> +{
>>> +	struct memblock_region *reg;
>>> +	struct crash_mem *tmem;
>>> +	int ret;
>>> +
>>> +	for_each_memblock(memory, reg) {
>>> +		u64 base, size;
>>> +
>>> +		base = (u64)reg->base;
>>> +		size = (u64)reg->size;
>>> +
>>> +		/* Skip backup memory region, which needs a separate entry */
>>> +		if (base == BACKUP_SRC_START) {
>>> +			if (size > BACKUP_SRC_SIZE) {
>>> +				base = BACKUP_SRC_END + 1;
>>> +				size -= BACKUP_SRC_SIZE;
>>> +			} else
>>> +				continue;
>>> +		}
>>> +
>>> +		ret = add_mem_range(mem_ranges, base, size);
>>> +		if (ret)
>>> +			goto out;
>>> +
>>> +		/* Try merging adjacent ranges before reallocation attempt */
>>> +		if ((*mem_ranges)->nr_ranges == (*mem_ranges)->max_nr_ranges)
>>> +			sort_memory_ranges(*mem_ranges, true);
>>> +	}
>>> +
>>> +	/* Reallocate memory ranges if there is no space to split ranges */
>>> +	tmem = *mem_ranges;
>>> +	if (tmem && (tmem->nr_ranges == tmem->max_nr_ranges)) {
>>> +		tmem = realloc_mem_ranges(mem_ranges);
>>> +		if (!tmem)
>>> +			goto out;
>>> +	}
>>> +
>>> +	/* Exclude crashkernel region */
>>> +	ret = crash_exclude_mem_range(tmem, crashk_res.start, crashk_res.end);
>>> +	if (ret)
>>> +		goto out;
>>> +
>>> +	ret = add_rtas_mem_range(mem_ranges);
>>> +	if (ret)
>>> +		goto out;
>>> +
>>> +	ret = add_opal_mem_range(mem_ranges);
>>> +	if (ret)
>>> +		goto out;
>> 
>> Maybe I'm confused, but don't you add the RTAS and OPAL regions as
>> usable memory for the crashkernel? In that case they shouldn't show up
>> in the core file.
>
> kexec-tools does the same thing. I am not endorsing it but I was trying to stay
> in parity to avoid breaking any userspace tools/commands. But as you rightly
> pointed, this is NOT right. The right thing to do, to get the rtas/opal data at
> the time of crash, is to have a backup region for them just like we have for
> the first 64K memory. I was hoping to do that later.
>
> Will check how userspace tools respond to dropping these regions. If that makes
> the tools unhappy, will retain the regions with a FIXME. Sorry about the confusion.

No problem, thanks for the clarification.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center