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

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Message-ID: <f745de42-297e-6eed-d25b-ea21d6000dc5@linux.ibm.com>
Date:   Mon, 29 Jun 2020 11:25:02 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     piliu <piliu@...hat.com>, Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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>,
        Dave Young <dyoung@...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



On 28/06/20 7:44 am, piliu wrote:
> Hi Hari,

Hi Pingfan,

> 
> After a quick through for this series, I have a few question/comment on
> this patch for the time being. Pls see comment inline.
> 
> On 06/27/2020 03:05 AM, 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.

[...]

>> +	/*
>> +	 * Use the locate_mem_hole logic in kexec_add_buffer() for regular
>> +	 * kexec_file_load syscall
>> +	 */
>> +	if (kbuf->image->type != KEXEC_TYPE_CRASH)
>> +		return 0;
> Can the ranges overlap [crashk_res.start, crashk_res.end]?  Otherwise
> there is no requirement for @exclude_ranges.

The ranges like rtas, opal are loaded by f/w. They almost always overlap with
crashkernel region. So, @exclude_ranges is required to support kdump.

> I guess you have a design for future. If not true, then it is better to
> fold the condition "if (kbuf->image->type != KEXEC_TYPE_CRASH)" into the
> caller and rename this function to better distinguish use cases between
> kexec and kdump

Yeah, this condition will be folded. I have a follow-up patch for that explaining
why kexec case should also be folded. Will try to add that to this series for v2.

Thanks
Hari