On 04.03.2024 17:46, Julien Grall wrote: > On 04/03/2024 16:41, Jan Beulich wrote: >> On 04.03.2024 17:31, Julien Grall wrote: >>> On 04/03/2024 16:10, Andrew Cooper wrote: >>>> It is daft to require all architectures to provide empty implementations of >>>> this functionality. >>> >>> Oleksii recenlty sent a similar patch [1]. This was pushed back because >>> from naming, it sounds like the helpers ought to be non-empty on every >>> architecture. >>> >>> It would be best if asm-generic provides a safe version of the helpers. >>> So my preference is to not have this patch. This can of course change if >>> I see an explanation why it is empty on Arm (I believe it should contain >>> csdb) and other arch would want the same. >> >> Except that there's no new asm-generic/ header here (as opposed to how >> Oleksii had it). Imo avoiding the need for empty stubs is okay this way, >> when introducing an asm-generic/ header would not have been. Of course >> if Arm wants to put something there rather sooner than later, then >> perhaps the functions better wouldn't be removed from there, just to then >> be put back pretty soon. > > I am confused. I agree the patch is slightly different, but I thought > the fundamental problem was the block_speculation() implementation may > not be safe everywhere. And it was best to let each architecture decide > how they want to implement (vs Xen decide for us the default). > > Reading the original thread, I thought you had agreed with that > statement. Did I misinterpret? Yes and no. Whatever is put in asm-generic/ ought to be correct and safe by default, imo. The same doesn't apply to fallbacks put in place in headers in xen/: If an arch doesn't provide its own implementation, it indicates that the default (fallback) is good enough. Still I can easily see that other views are possible here ...
Jan
