On 30.09.19 17:03, Richard Henderson wrote: > On 9/30/19 12:55 AM, David Hildenbrand wrote: >>> What I think you should do instead is check env_neg(env)->icount_decr, >>> exactly >>> like we do at the start of every basic block, and use that as an indication >>> that you should exit back to the main loop. >> >> The issue is that when we return to the main loop we really have to >> inject an interrupt - otherwise we might simply skip parts of the >> (interruptible) instruction and continue with the next one. > > Do we? We will return to the main loop with psw.addr still pointing at MVCL, > so the interrupt is delivered, and when the exception returns we restart the > MVCL. Or, an interrupt is not delivered and we restart from psw.addr and > still > restart the MVCL.
If that's the case, then this should indeed work. > > We probably would have to take a hard look at EXECUTE of MVCL to see if that > is > actually restartable. Not that it makes particular sense to want that combo, > but it's required to work. > Yes, this has to work. I'll look into that once I have some time. >> However, with I/O interrupts, we can actually race against other VCPUs. >> So the I/O interrupt might be gone by the time we arrive in the main loop. > > Of course, but it's no different with this case than any other. If the > interrupt has already been handled, then we will simply restart the next TB as > per normal. Yeah, I was mostly concerned that "the next TB" will be "the next instruction" and not "the original instruction again". -- Thanks, David / dhildenb
