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 15:40:12 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Hari Bathini <hbathini@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pingfan Liu <piliu@...hat.com>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Petr Tesarik <ptesarik@...e.cz>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH 04/11] ppc64/kexec_file: avoid stomping memory used by
 special regions

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?

Thanks
Dave