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

From: piliu <piliu@redhat.com>
To: Hari Bathini <hbathini@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Kexec-ml <kexec@lists.infradead.org>,
	Petr Tesarik <ptesarik@suse.cz>,
	Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
	Sourabh Jain <sourabhjain@linux.ibm.com>,
	lkml <linux-kernel@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@ozlabs.org>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Thiago Jung Bauermann <bauerman@linux.ibm.com>,
	Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>
Subject: Re: [PATCH 04/11] ppc64/kexec_file: avoid stomping memory used by special regions
Date: Tue, 30 Jun 2020 16:13:04 +0800	[thread overview]
Message-ID: <aa6d91e7-b7c2-0e46-f446-a065d2db4b52@redhat.com> (raw)
In-Reply-To: <cca6a693-a77f-885e-8ccc-967953f53800@linux.ibm.com>


On 06/30/2020 02:10 PM, Hari Bathini wrote:
> 
> 
> On 30/06/20 9:00 am, piliu wrote:
>>
>>
>> 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?
> 
> It does. Actually, reserve_map + reserved-ranges are reserved as soon as
> memblock allocator is ready but not before crashkernel reservation.
> Check early_reserve_mem() call in kernel/prom.c
> 
>> 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?
> 
> So, kdump could possibly overwrite these regions which is why an exclude
> range list is needed. Same thing was done in kexec-tools as well.
OK, got it.

Thanks,
Pingfan
> 
> Thanks
> Hari
> 
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