linux-kernel - Re: [PATCH v18 02/17] x86/setup: Move xen_pv_domain() check and insert_resource() to setup

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Date:   Fri, 7 Jan 2022 16:13:00 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        <kexec@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, "Jonathan Corbet" <corbet@....net>,
        <linux-doc@...r.kernel.org>, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        "John Donnelly" <John.p.donnelly@...cle.com>
Subject: Re: [PATCH v18 02/17] x86/setup: Move xen_pv_domain() check and
 insert_resource() to setup_arch()



On 2021/12/25 9:53, Leizhen (ThunderTown) wrote:
> 
> 
> On 2021/12/24 14:36, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2021/12/24 1:26, Borislav Petkov wrote:
>>> On Wed, Dec 22, 2021 at 09:08:05PM +0800, Zhen Lei wrote:
>>>> From: Chen Zhou <chenzhou10@...wei.com>
>>>>
>>>> We will make the functions reserve_crashkernel() as generic, the
>>>> xen_pv_domain() check in reserve_crashkernel() is relevant only to
>>>> x86,
>>>
>>> Why is that so? Is Xen-PV x86-only?
>>>
>>>> the same as insert_resource() in reserve_crashkernel[_low]().
>>>
>>> Why?
>>>
>>> Looking at
>>>
>>>   0212f9159694 ("x86: Add Crash kernel low reservation")
>>>
>>> it *surprisingly* explains why that resources thing is being added:
>>>
>>>     We need to add another range in /proc/iomem like "Crash kernel low",
>>>     so kexec-tools could find that info and append to kdump kernel
>>>     command line.
>>>
>>> Then,
>>>
>>>   157752d84f5d ("kexec: use Crash kernel for Crash kernel low")
>>>
>>> renamed it because, as it states, kexec-tools was taught to handle
>>> multiple resources of the same name.
>>>
>>> So why does kexec-tools on arm *not* need those iomem resources? How
>>> does it parse the ranges there? Questions over questions...

Hi Borislav:
  The reason why insert_resource() cannot be used in reserve_crashkernel[_low]()
on arm64 is clear. The parent resource node of crashk[_low]_res is added by
request_resource() in request_standard_resources(), so that it will be conflicted.
All request_resource() in request_standard_resources() should be changed to
insert_resource(), to make insert_resource() can be used in reserve_crashkernel[_low]().

  I found commit e25e6e7593ca ("kdump, x86: Process multiple Crash kernel in /proc/iomem")
in kexec-tools. I'm trying to port it to arm64, or make it generic.

  Thanks.

> 
> It's a good question worth figuring out. I'm going to dig into this.
> I admire your rigorous style and sharp vision.
> 


-- 
Regards,
  Zhen Lei