Re: [PATCH v8 6/7] apei/ghes: Use unrcu_pointer for cmpxchg

Borislav Petkov
2022-10-14T19:40:39Z

On Fri, Oct 14, 2022 at 11:40:39AM +0200, Ard Biesheuvel wrote:
> The cache struct pointer should not be published until after the
> struct itself is fully populated. So on the producer side, some kind
> of hardware barrier is definitely needed, or the struct may appear
> half-baked to other cores that can read the updated pointer.

Ah, right you are, ghes_estatus_cached() is called in all kinds of
contexts and by other cores, sure.

> OTOH the code seems to be working fine as is, so why modify it at all?
> (apart from the purely cosmetic changes)

peterz questioned that smp_wmb() there and then we started digging. And
frankly, even if removing that barrier won't make any difference, I'd
still prefer it gone and have the code simpler and cleaner.

Thx.

--
Regards/Gruss,
Boris.