Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region support through command line

Mukesh Ojha
2023-10-05T16:19:05Z

On 10/5/2023 5:14 PM, Pavan Kondeti wrote:
> On Thu, Oct 05, 2023 at 04:52:20PM +0530, Mukesh Ojha wrote:
>> Sorry for the late reply, was on a long vacation.
>>
>> On 9/14/2023 4:47 AM, Kees Cook wrote:
>>> On Tue, Sep 12, 2023 at 11:18:20AM +0100, Will Deacon wrote:
>>>> On Mon, Sep 11, 2023 at 04:23:50PM +0530, Mukesh Ojha wrote:
>>>>> The reserved memory region for ramoops is assumed to be at a fixed
>>>>> and known location when read from the devicetree. This may not be
>>>>> required for something like Qualcomm's minidump which is interested
>>>>> in knowing addresses of ramoops region but it does not put hard
>>>>> requirement of address being fixed as most of it's SoC does not
>>>>> support warm reset and does not use pstorefs at all instead it has
>>>>> firmware way of collecting ramoops region if it gets to know the
>>>>> address and register it with apss minidump table which is sitting
>>>>> in shared memory region in DDR and firmware will have access to
>>>>> these table during reset and collects it on crash of SoC.
>>>>>
>>>>> So, add the support of reserving ramoops region to be dynamically
>>>>> allocated early during boot if it is request through command line
>>>>> via 'dyn_ramoops_size=' and fill up reserved resource structure and
>>>>> export the structure, so that it can be read by ramoops driver.
>>>>>
>>>>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>>>>> ---
>>>>> arch/arm64/mm/init.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>
>>>> Why does this need to be in the arch code? There's absolutely nothing
>>>> arm64-specific here.
>>>
>>> I would agree: this needs to be in ramoops itself, IMO. It should be a
>>> ramoops module argument, too.
>>>
>>> It being unhelpful for systems that don't have an external consumer is
>>> certainly true, but I think it would still make more sense for this
>>> change to live entirely within ramoops. Specifically: you're
>>> implementing a pstore backend behavioral change. In the same way that
>>> patch 10 is putting the "output" side of this into pstore/, I'd expect
>>> the "input" side also in pstore/
>>
>> How do we reserve memory? are you suggesting to use dma api's for
>> dynamic ramoops ?
>>
> Sharing my thoughts:
>
> Your patch is inspired from how kexec allocate memory for crash kernel
> right?

Yes.

> There is a series [1] which moved arch code (ARM64/x86) to
> generic kexec core. Something we should also do as the feedback
> received here.
>
> Coming to how part, we still have to use memblock API to increase the chance
> of allocating contiguous memory. Since PSTORE_RAM can also be
> compiled as a module, we probably need another pstore layer that needs to
> be built statically in kernel to allocate memory using memblock API.
> once slab is available, all memblock API will re-direct to slab
> allocations. This layer can be enabled via ARCH_WANTS_PSTORE_xxx or
> another config that only supports 'y'. PSTORE_RAM can still be a module but
> when this layer is available, it supports dynamic ramoops. Another option
> would be just including this layer in PSTORE RAM module but take away module
> option when this layer is enabled.

I thought about this but still the caller will be in Arch code,
right ? would that be fine with others ?

-Mukesh
>
>
> [1]
> https://lore.kernel.org/all/20211020020317.1220-6-thunder.leizhen@huawei.com/