On 04/05/2018 12:38, Alexander Shishkin wrote: >>> Or rather a parameter to decide who wins in case both host and guest want >>> to trace the guest. That's arguably better than having different versions of >>> PT in the guest depending on a module parameter setting. >> It's not different versions; it's having PT vs. not having PT at all. I >> don't really see it as a big issue. The nice thing about this series is >> that the interactions between PT code and KVM code are minimal. > Unfortunately, it gets it wrong. Like I just said in another email, if you > switch off host's PT, you need to let them know, which this patchset doesn't > do. And when it does, it would be the same amount of interaction with PT > code as what would be required to get the dynamic guest PT right. Two issues: 1) Is there a fast (10 clock cycles, better if less) way for KVM to know "PT is enabled on the host", or a callback that KVM can register when e.g. RTIT_CTL is written? 2) We'd have to write trace records into the guest. That does not sound that easy. Does it entail parsing the ToPA and all that? Thanks, Paolo
