Re: [PATCH] arm64: Add the arm64.nolse_atomics command line option

Aiqun(Maria) Yu
2023-07-11T04:03:13Z

On 7/10/2023 5:37 PM, Will Deacon wrote:
> On Mon, Jul 10, 2023 at 01:59:55PM +0800, Maria Yu wrote:
>> In order to be able to disable lse_atomic even if cpu
>> support it, most likely because of memory controller
>> cannot deal with the lse atomic instructions, use a
>> new idreg override to deal with it.
>
> This should not be a problem for cacheable memory though, right?
>
> Given that Linux does not issue atomic operations to non-cacheable mappings,
> I'm struggling to see why there's a problem here.

The lse atomic operation can be issued on non-cacheable mappings as
well. Even if it is cached data, with different CPUECTLR_EL1 setting, it
can also do far lse atomic operations.

>
> Please can you explain the problem that you are trying to solve?

In our current case, it is a 100% reproducible issue that happened for
uncached data, the cpu which support LSE atomic, but the system's DDR
subsystem is not support this and caused a NOC error and thus
synchronous external abort happened.
>
> Will