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

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Date:   Tue, 30 Jun 2020 11:30:26 +0800
From:   piliu <piliu@...hat.com>
To:     Hari Bathini <hbathini@...ux.ibm.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 06/29/2020 01:55 PM, Hari Bathini wrote:
> 
> 
> 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.
f/w passes rtas/opal as service, then must f/w mark these ranges as
fdt_reserved_mem in order to make kernel aware not to use these ranges?
Otherwise kernel memory allocation besides kdump can also overwrite
these ranges.

Hmm, revisiting reserve_crashkernel(). It seems not to take any reserved
memory into consider except kernel text. Could it work based on memblock
allocator?

Thanks,
Pingfan
> 
>> 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
>