tor 2019-10-03 klockan 09:45 -0400 skrev Paul Koning via cctalk: > > On Oct 3, 2019, at 8:25 AM, Maciej W. Rozycki <ma...@linux-mips.org > > > wrote: > > > > On Thu, 3 Oct 2019, Maciej W. Rozycki wrote: > > > > > > You need an extremely high resolution timer to detect slight > > > > differences in > > > > execution time of speculatively-executed threads. The VAX > > > > 11/780 certainly did > > > > not do speculative execution, and my guess is that all VAXen > > > > did not, either. > > > > > > The NVAX and NVAX+ implementations include a branch predictor in > > > their > > > microarchitecture[1], so obviously they do execute speculatively. > > > > For the record: in NVAX prediction does not extend beyond the > > instruction > > fetch unit (I-box in VAX-speak), so there's actually no > > speculative > > execution, but only speculative prefetch. > > That's a key point. These vulnerabilities are quite complex and > details matter. They depend on speculation that goes far enough to > make data references that produce cache fills, and that those fills > persist after the speculative references have been voided. > > Branch prediction is only the first step, and as you point out, that > alone is nowhere near enough. For example, if a particular design > did speculative execution but not speculative memory references on > adresses that miss in the cache, you'd still have no issue. >
Can the speculative pre-fetch of instruction trigger cache fills ?