[PATCH v8 13/14] RISC-V: KVM: add support for FWFT SBI extension

[Radim Krčmář]

2025-05-23T11:02:11-07:00, Atish Patra <atish.patra at linux.dev>:
> On 5/23/25 9:27 AM, Radim KrÄmáŠwrote:
>> 2025-05-23T17:29:49+02:00, Clément Léger <cleger at rivosinc.com>:
>>> Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
>>> is ratified so that would be nice not delaying it too much. I'll take a
>>> look at it to see if it isn't too long to implement.
>> 
>> Not blocking, but I would at least default FWFT to disabled, because
>> current userspace cannot handle [14/14].  (Well... save/restore was
>> probably broken even before, but let's try to not make it worse. :])
>> 
>
> User space can not enable or disable misaligned access delegation as 
> there is no interface for now rightly pointed by you.

I mean setting default_disabled=true and just disabling FWFT for the
guest unless userspace explicitly enables the incomplete extension.
We would blame the user for wanting mutually exclusive features.

>                                                       I guess supporting 
> that would be quicker than fixing the broader guest save/restore 
> anyways. Isn't it ?

Yes.  The save/restore for FWFT is simple (if we disregard the
discussions), but definitely more than a single line.