linux-kernel - Re: [PATCH v3 03/12] powerpc/kexec_file: add helper functions for getting memory ranges

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Message-ID: <1b09c0e4-54c9-7dd6-4402-81c9d1ba3ee0@linux.ibm.com>
Date:   Sat, 18 Jul 2020 01:30:13 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     Pingfan Liu <piliu@...hat.com>, Petr Tesarik <ptesarik@...e.cz>,
        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>,
        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 03/12] powerpc/kexec_file: add helper functions for
 getting memory ranges



On 17/07/20 10:02 am, Hari Bathini wrote:
> 
> 
> On 15/07/20 5:19 am, Thiago Jung Bauermann wrote:
>>
>> Hello Hari,
>>
>> Hari Bathini <hbathini@...ux.ibm.com> writes:
>>
>>> In kexec case, the kernel to be loaded uses the same memory layout as
>>> the running kernel. So, passing on the DT of the running kernel would
>>> be good enough.
>>>
>>> But in case of kdump, different memory ranges are needed to manage
>>> loading the kdump kernel, booting into it and exporting the elfcore
>>> of the crashing kernel. The ranges are exlude memory ranges, usable
>>
>> s/exlude/exclude/
>>
>>> memory ranges, reserved memory ranges and crash memory ranges.
>>>
>>> Exclude memory ranges specify the list of memory ranges to avoid while
>>> loading kdump segments. Usable memory ranges list the memory ranges
>>> that could be used for booting kdump kernel. Reserved memory ranges
>>> list the memory regions for the loading kernel's reserve map. Crash
>>> memory ranges list the memory ranges to be exported as the crashing
>>> kernel's elfcore.
>>>
>>> Add helper functions for setting up the above mentioned memory ranges.
>>> This helpers facilitate in understanding the subsequent changes better
>>> and make it easy to setup the different memory ranges listed above, as
>>> and when appropriate.
>>>
>>> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
>>> Tested-by: Pingfan Liu <piliu@...hat.com>
>>
> 
> <snip>
> 
>>> +/**
>>> + * add_reserved_ranges - Adds "/reserved-ranges" regions exported by f/w
>>> + *                       to the given memory ranges list.
>>> + * @mem_ranges:          Range list to add the memory ranges to.
>>> + *
>>> + * Returns 0 on success, negative errno on error.
>>> + */
>>> +int add_reserved_ranges(struct crash_mem **mem_ranges)
>>> +{
>>> +	int i, len, ret = 0;
>>> +	const __be32 *prop;
>>> +
>>> +	prop = of_get_property(of_root, "reserved-ranges", &len);
>>> +	if (!prop)
>>> +		return 0;
>>> +
>>> +	/*
>>> +	 * Each reserved range is an (address,size) pair, 2 cells each,
>>> +	 * totalling 4 cells per range.
>>
>> Can you assume that, or do you need to check the #address-cells and
>> #size-cells properties of the root node?
> 
> Taken from early_reserve_mem_dt() which did not seem to care.
> Should we be doing any different here?

On second thoughts, wouldn't hurt to be extra cautious. Will use
#address-cells & #size-cells to parse reserved-ranges.

Thanks
Hari