Re: [PATCH 1/2] arm64: Reduce add_map() complexity

Pierre-Clément Tosi
2024-03-15T15:13:19Z

Hi Fabio,

On Fri, Mar 15, 2024 at 08:56:17AM -0300, Fabio Estevam wrote:
> Hi Marc,
>
> On Sat, Mar 9, 2024 at 11:36 AM Fabio Estevam <festevam@gmail.com> wrote:
>
> > Does the log below help?
> >
> > https://pastebin.com/raw/1i1VBA0a
> >
> > If not, please send me a debug patch and I will be glad to run it here.
>
> I'm sorry to bother you, but have you had a chance to look at the log
> I shared with you?

I had a quick look through your logs and notice that U-Boot master attempts to
map addresses in the high VA range e.g.

Checking if pte fits for virt=ffffffffe4000000 [...]

while the logs that boot successfully only use the low VA range e.g.

Checking if pte fits for virt=80193000 [...]

Unless that has recently changed (since I last worked with U-Boot), U-Boot on
AArch64 only supports identity mappings and therefore was only taught how to
program TTBR0_ELx (i.e. is only able to map low virtual addresses). This means
that the code - with or without 41e2787f5ec4 - would be unable to map addresses
such as 0xffffffffe4000000.

Now, given that 41e2787f5ec4 only affects implementation details of add_map(),
I am surprised that reverting that commit changes the arguments received by the
function such as virt. As a reminder, add_map() is exclusively used on mem_map:

for (i = 0; mem_map[i].size || mem_map[i].attrs; i++)
add_map(&mem_map[i]);

>
> That's the only issue preventing colibri-imx8x from booting mainline U-Boot.

If I read the U-Boot configs right i.e.

- configs/colibri-imx8x_defconfig: CONFIG_ARCH_IMX8=y
- arch/arm/mach-imx/imx8/Makefile: obj-y += cpu.o
- arch/arm/mach-imx/imx8/cpu.c: struct mm_region *mem_map = imx8_mem_map;

There is a possibility that your mem_map is getting modified by MACH-specific
code. In particular, enable_caches() seems to dynamically get the MMU mappings
from some RPC mechanism (see get_owned_memreg() and sc_rm_get_memreg_info()).

Could it be that whatever services those requests might be returning unexpected
values? Instrumenting arch/arm/mach-imx/imx8/cpu.c and dumping mem_map (and
the RPC messages) with/without the patch would help clear this up.

HTH,

>
> We would like to get this fixed for U-Boot 2024.04.
>
> Thanks for your help

--
Pierre