[PATCH v1] arm: add call to cleanup_before_linux for go command

[Tom Rini]

On Wed, Apr 30, 2025 at 09:27:30PM +0530, Anshul Dalal wrote:
> On Wed Apr 30, 2025 at 7:46 PM IST, Tom Rini wrote:
> > On Wed, Apr 30, 2025 at 07:27:50PM +0530, Anshul Dalal wrote:
> >
> >> As discussed here[1], the go command causes undefined behavior when used
> >> for running custom OSes since the icache might hold outdated data. OSes
> >> usually also expect the MMU to be disabled upon execution.
> >> 
> >> Therefore this patch adds a call to cleanup_before_linux before we jump
> >> to the loaded program/os which disables both the caches and the MMU.
> >> This makes the go command's behavior consistent with riscv platforms.
> >> 
> >> NOTE: This might cause regressions with users expecting a configured MMU
> >> but I'm unsure if it's a supported use case for the go command anyway.
> >> 
> >> [1]: https://lore.kernel.org/u-boot/D9DXL95MTQ8I.3EUY0C6M2L4NE@ti.com/
> >> 
> >> Signed-off-by: Anshul Dalal <anshuld at ti.com>
> >
> > This is the inverse of what needs to be done, sorry. RISC-V shouldn't be
> > doing this type of cleanup. I know it sounds reductive but "go means
> > go". We have all of the other bootX commands for "prepare the system and
> > boot the thing at $address".
> 
> Well, "go means go" implies we jump to the necessary DDR address and
> start executing. But with caches enabled, it fails in cases where we
> have that specific address in the icache already. In that case the
> execution starts from whatever's stored in the icache and not really
> DDR.

Yes, and if you're using go you're supposed to disable the cache and
force a flush. Or you're doing something Interesting and nothing else
should be getting in the way.

-- 
Tom
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