linux-kernel - Re: [PATCH v2] of/fdt: add dt_phys arg to early_init_dt_scan and early_init_dt

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Message-ID: <71decb01-4241-4fb0-bc38-187e180d6ee5@gmail.com>
Date: Mon, 28 Oct 2024 10:49:40 +0000
From: Usama Arif <usamaarif642@...il.com>
To: Rob Herring <robh@...nel.org>
Cc: mark.rutland@....com, will@...nel.org, leitao@...ian.org,
 catalin.marinas@....com, tglx@...utronix.de, chris@...kel.net,
 saravanak@...gle.com, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 kexec@...ts.infradead.org, loongarch@...ts.linux.dev,
 linux-sh@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, linux-openrisc@...r.kernel.org,
 linux-mips@...r.kernel.org, linux-csky@...r.kernel.org
Subject: Re: [PATCH v2] of/fdt: add dt_phys arg to early_init_dt_scan and
 early_init_dt_verify



On 25/10/2024 23:15, Rob Herring wrote:
> On Wed, Oct 23, 2024 at 12:14 PM Usama Arif <usamaarif642@...il.com> wrote:
>>
>>  __pa() is only intended to be used for linear map addresses and using
>> it for initial_boot_params which is in fixmap for arm64 will give an
>> incorrect value. Hence save the physical address when it is known at
>> boot time when calling early_init_dt_scan for arm64 and use it at kexec
>> time instead of converting the virtual address using __pa().
>>
>> Reported-by: Breno Leitao <leitao@...ian.org>
>> Suggested-by: Mark Rutland <mark.rutland@....com>
>> Signed-off-by: Usama Arif <usamaarif642@...il.com>
>> Fixes: ac10be5cdbfa ("arm64: Use common of_kexec_alloc_and_setup_fdt()")
> 
> This looks fine, but what is the symptom without this compared to
> before the above change? The original code in the referenced commit
> above didn't remove the reservation at all. Unless the current code
> does something worse, this is new functionality more than a fix (for
> stable).
> 
> Rob

After the series in [1] was merged, we always get a warning when kexecing
a debug kernel, which was reported by Breno in [2].
The issue is using __pa for a fixmap address in arm64 as described in [2],
which could result in removing a memory reservation for a completely
unrelated area.
That was introduced by the patch just before 
"arm64: Use common of_kexec_alloc_and_setup_fdt" [3], but arm64 switched to
using the common kexec fdt function in that commit. This commit is trying
to fix removing and corrupting any random memory reservation (and get rid
of the warning) that was introduced by [1], not adding a new functionality.

[1] https://lore.kernel.org/all/20210221174930.27324-7-nramas@linux.microsoft.com/ 
[2] https://lore.kernel.org/all/ZnFKEtqfqJkYflwL@gmail.com/
[3] https://lore.kernel.org/all/20210221174930.27324-6-nramas@linux.microsoft.com/

Thanks,
Usama