Re: [PATCH] riscv: Enable interrupt during exception handling

["Clément Léger" <cleger@rivosinc.com>]

On 24/06/2025 15:17, Nam Cao wrote:
> On Tue, Jun 24, 2025 at 01:37:13PM +0200, Clément Léger wrote:
>> On 24/06/2025 04:09, Maciej W. Rozycki wrote:
>>> On Mon, 23 Jun 2025, Palmer Dabbelt wrote:
>>>> I'm kind of split on a Fixes tag here.  One could argue it's a regression, as
>>>> having interrupts disabled during exceptions is going to cause all sorts of
>>>> performance issues for users.  Seems a bit risk to just backport, though...
>>>>
>>>> That said, if nobody noticed then it's probably a good sign nobody is really
>>>> paying attention and we should just backport it before anyone notices...
>>>
>>>  Oh, someone did notice and it's not only performance, cf. 
>>> <https://lore.kernel.org/r/alpine.DEB.2.21.2501070143250.18889@angie.orcam.me.uk/>.
>>
>> I also had a series which was doing so for misaligned accesses handling,
>> but after discussion, it was not ok to do so.:
>>
>> https://lore.kernel.org/linux-riscv/20250422094419.GC14170@noisy.programming.kicks-ass.net/
> 
> If I understand that right, exceptions from kernel should be treated as
> NMI, so that lockdep can tell us if exception handlers touch locks.
> 
> But (conditionally) enabling interrupts does not lose us that benefit. It
> is still considered NMI by lockdep.
> 
> Unless I miss something, the patch is fine as is.

Hi Nam,

Yeah indeed, providing that all traps handlers really are reentrant, I
think it's fine.

Thanks,

Clément

> 
> Best regards,
> Nam