linux-kernel - Re: [PATCH v9 07/11] arm64: kexec

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Date:   Thu, 24 May 2018 09:25:43 -0500
From:   Rob Herring <robh@...nel.org>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Rob Herring <robh@...nel.org>,
        James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Howells <dhowells@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>, dyoung@...hat.com,
        Baoquan He <bhe@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        bhsharma@...hat.com, kexec@...ts.infradead.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v9 07/11] arm64: kexec_file: add crash dump support

On Mon, May 21, 2018 at 5:14 AM, AKASHI Takahiro
<takahiro.akashi@...aro.org> wrote:
> Hi Rob,
>
> On Fri, May 18, 2018 at 10:35:52AM -0500, Rob Herring wrote:
>> On Tue, May 15, 2018 at 06:12:59PM +0100, James Morse wrote:
>> > Hi guys,
>> >
>> > (CC: +RobH, devicetree list)
>>
>> Thanks.
>>
>> > On 25/04/18 07:26, AKASHI Takahiro wrote:
>> > > Enabling crash dump (kdump) includes
>> > > * prepare contents of ELF header of a core dump file, /proc/vmcore,
>> > >   using crash_prepare_elf64_headers(), and
>> > > * add two device tree properties, "linux,usable-memory-range" and
>> > >   "linux,elfcorehdr", which represent repsectively a memory range
>> > >   to be used by crash dump kernel and the header's location
>>
>> BTW, I intend to move existing parsing these out of the arch code.
>> Please don't add more DT handling to arch/ unless it is *really* arch
>> specific. I'd assume that the next arch to add kexec support will use
>> these bindings instead of the powerpc way.
>
> So do you expect all the fdt-related stuff in my current implementation
> for arm64 to be put into libfdt, or at least drivers/of, from the beginning?

Yes.

> I'm not sure how arch-specific the properties here are. For instance,
> it is only arm64 that uses "linux,usable-memory-range" right now but
> if some other arch follows, it is no more arch-specific.
> # I remember that you didn't like this property :)

The question I guess is what will the next arch use. I don't think any
other DT based arch supports crashdump or kexec yet.

>> > > +{
>> > > + void *buf, *prop;
>> > > + size_t buf_size;
>> > > + int result;
>> > > +
>> > > + buf_size = (__dt_root_addr_cells + __dt_root_size_cells) * sizeof(u32);
>> > > + prop = buf = vmalloc(buf_size);
>>
>> This can go on the stack instead (and would be required to to work in
>> libfdt).
>
> Well, I can't agree with you here since we are now in effort, as far as
> I correctly understand, of purging all the variable-sized arrays on a local
> stack out of the kernel code.

You don't need a variable sized array. The array size just needs to
the the maximum size (16 bytes).

Rob