On 01.03.2022 15:39, Andrew Cooper wrote: > On 01/03/2022 14:14, Jan Beulich wrote: >> On 01.03.2022 14:07, Andrew Cooper wrote: >>> On 01/03/2022 11:05, Jan Beulich wrote: >>> That said... what's wrong a plain NULL? I can't see any need for a >>> magic constant here. >> Are you fancying an XSA for a call through NULL in PV guest context? > > Why do you think that a risk? Only non-NULL function pointers are > followed, and altcall resolves safely if the pointer is still NULL. > > And on that subject, don't we not hit the altcall's BUG_ON() for > exceeding disp32?
There's no altcall involved here. As said in earlier contexts, altcall patching comes to early to cover plt_tsc use. Hence the only concern is a non-altacll-ed use of the pointer. Jan
