linux-kernel - Re: [PATCH 04/11] ppc64/kexec_file: avoid stomping memory used by special regions

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Date:   Wed, 1 Jul 2020 20:53:35 +0800
From:   piliu <piliu@...hat.com>
To:     Dave Young <dyoung@...hat.com>,
        Hari Bathini <hbathini@...ux.ibm.com>
Cc:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH 04/11] ppc64/kexec_file: avoid stomping memory used by
 special regions



On 07/01/2020 03:40 PM, Dave Young wrote:
> Hi Hari,
> On 06/27/20 at 12:35am, Hari Bathini wrote:
>> crashkernel region could have an overlap with special memory regions
>> like  opal, rtas, tce-table & such. These regions are referred to as
>> exclude memory ranges. Setup this ranges during image probe in order
>> to avoid them while finding the buffer for different kdump segments.
>> Implement kexec_locate_mem_hole_ppc64() that locates a memory hole
>> accounting for these ranges. Also, override arch_kexec_add_buffer()
>> to locate a memory hole & later call __kexec_add_buffer() function
>> with kbuf->mem set to skip the generic locate memory hole lookup.
>>
>> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
>> ---
>>  arch/powerpc/include/asm/crashdump-ppc64.h |   10 +
>>  arch/powerpc/include/asm/kexec.h           |    7 -
>>  arch/powerpc/kexec/elf_64.c                |    7 +
>>  arch/powerpc/kexec/file_load_64.c          |  292 ++++++++++++++++++++++++++++
>>  4 files changed, 312 insertions(+), 4 deletions(-)
>>  create mode 100644 arch/powerpc/include/asm/crashdump-ppc64.h
>>
> [snip]
>>  /**
>> + * get_exclude_memory_ranges - Get exclude memory ranges. This list includes
>> + *                             regions like opal/rtas, tce-table, initrd,
>> + *                             kernel, htab which should be avoided while
>> + *                             setting up kexec load segments.
>> + * @mem_ranges:                Range list to add the memory ranges to.
>> + *
>> + * Returns 0 on success, negative errno on error.
>> + */
>> +static int get_exclude_memory_ranges(struct crash_mem **mem_ranges)
>> +{
>> +	int ret;
>> +
>> +	ret = add_tce_mem_ranges(mem_ranges);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_initrd_mem_range(mem_ranges);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_htab_mem_range(mem_ranges);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_kernel_mem_range(mem_ranges);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_rtas_mem_range(mem_ranges, false);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_opal_mem_range(mem_ranges, false);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = add_reserved_ranges(mem_ranges);
>> +	if (ret)
>> +		goto out;
>> +
>> +	/* exclude memory ranges should be sorted for easy lookup */
>> +	sort_memory_ranges(*mem_ranges);
>> +out:
>> +	if (ret)
>> +		pr_err("Failed to setup exclude memory ranges\n");
>> +	return ret;
>> +}
> 
> I'm confused about the "overlap with crashkernel memory", does that mean
> those normal kernel used memory could be put in crashkernel reserved
> memory range?  If so why can't just skip those areas while crashkernel
> doing the reservation?
I raised the same question in another mail. As Hari's answer, "kexec -p"
skips these ranges in user space. And the same logic should be done in
"kexec -s -p"

Regards,
Pingfan