On Fri, Apr 19, 2024, Wei Wang wrote: > KVM_X86_OP and KVM_X86_OP_OPTIONAL were utilized to define and execute > static_call_update() calls on mandatory and optional hooks, respectively. > Mandatory hooks were invoked via static_call() and necessitated definition > due to the presumption that an undefined hook (i.e., NULL) would cause > static_call() to fail. This assumption no longer holds true as > static_call() has been updated to treat a "NULL" hook as a NOP on x86. > Consequently, the so-called mandatory hooks are no longer required to be > defined, rendering them non-mandatory. This is wrong. They absolutely are mandatory. The fact that static_call() doesn't blow up doesn't make them optional. If a vendor neglects to implement a mandatory hook, KVM *will* break, just not immediately on the static_call(). The static_call() behavior is actually unfortunate, as KVM at least would prefer that it does explode on a NULL point. I.e. better to crash the kernel (hopefully before getting to production) then to have a lurking bug just waiting to cause problems. > This eliminates the need to differentiate between mandatory and optional > hooks, allowing a single KVM_X86_OP to suffice. > > So KVM_X86_OP_OPTIONAL and the WARN_ON() associated with KVM_X86_OP are > removed to simplify usage, Just in case it isn't clear, I am very strongly opposed to removing KVM_X86_OP_OPTIONAL() and the WARN_ON() protection to ensure mandatory ops are implemented.
