[PATCH 1/3] arm64: Use FEAT_HAFDBS to track dirty pages when available

[Chris Packham]

On Sun, Oct 15, 2023 at 10:29 AM Chris Packham <judge.packham at gmail.com> wrote:
>
>
>
> On Sat, 14 Oct 2023, 11:04 am Marc Zyngier, <maz at kernel.org> wrote:
>>
>> On 2023-10-13 03:40, Chris Packham wrote:
>> > Hi Marc, Paul,
>> >
>> > On Sat, Mar 18, 2023 at 5:23 AM Ying-Chun Liu (PaulLiu)
>> > <paul.liu at linaro.org> wrote:
>> >>
>> >> From: Marc Zyngier <maz at kernel.org>
>> >>
>> >> Some recent arm64 cores have a facility that allows the page
>> >> table walker to track the dirty state of a page. This makes it
>> >> really efficient to perform CMOs by VA as we only need to look
>> >> at dirty pages.
>> >>
>> >> Signed-off-by: Marc Zyngier <maz at kernel.org>
>> >> [ Paul: pick from the Android tree. Rebase to the upstream ]
>> >> Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu at linaro.org>
>> >> Cc: Tom Rini <trini at konsulko.com>
>> >> Link:
>> >> https://android.googlesource.com/platform/external/u-boot/+/3c433724e6f830a6b2edd5ec3d4a504794887263
>> >
>> > I think this may have caused a regression for the Marvell AC5X
>> > board(s). I found that v2023.07 locked up at boot but v2023.01 was
>> > fine. The lockup seemed to be in the 'Net:' init probably just as the
>> > mvneta driver was being initialised.
>> >
>> > A git bisect led me to this change although for this specific change
>> > instead of the lockup I get a crash so maybe I'm actually hitting a
>> > different issue.
>> >
>> > Any thoughts as to why this may have caused problems?
>>
>> Not really. What CPUs does this platform have? What is the offending
>> driver doing to trigger the issue? Can you provide some level of
>> tracing?
>
>
> The Marvell AC5X is a network switch ASIC with an integrated ARMv8 CPU (8.1 specifically I think).
>
> I think there is something that the mvneta driver is doing triggering the issue. I have another AC5X based board without an Ethernet port that boots just fine (this is also why I didn't notice earlier).
>
> I'll try and get some more debug out when I'm back in the office
>

The thing the mvneta driver does that upsets things appears to be

    mmu_set_region_dcache_behaviour((phys_addr_t)bd_space, BD_SPACE,
                                                          DCACHE_OFF);

I can comment that line out and everything works.