On Mon, Oct 24, 2022, Maxim Levitsky wrote: > On Thu, 2022-10-20 at 19:14 +0000, Sean Christopherson wrote: > > On Thu, Oct 20, 2022, Maxim Levitsky wrote: > > > + // ensure that a pending timer is serviced > > > + irq_enable(); > > > > Jumping back to the "nop" patch, I'm reinforcing my vote to add sti_nop(). I > > actually starting typing a response to say this is broken before remembering that > > a nop got added to irq_enable(). > > OK, although, for someone that doesn't know about the interrupt shadow (I > guess most of the people that will look at this code), the above won't > confuse them, in fact sti_nop() might confuse someone who doesn't know about > why this nop is needed. The difference is that sti_nop() might leave unfamiliar readers asking "why", but it won't actively mislead them. And the "why" can be easily answered by a comment above sti_nop() to describe its purpose. A "see also safe_halt()" with a comment there would be extra helpful, as "safe halt" is the main reason the STI shadow is even a thing. On the other hand, shoving a NOP into irq_enable() is pretty much guaranteed to cause problems for readers that do know about STI shadows since there's nothing in the name "irq_enable" that suggests that the helper also intentionally eats the interrupt shadow, and especically because the kernel's local_irq_enable() distills down to a bare STI.
