> On Jul 15, 2020, at 3:21 PM, Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> wrote: > > > On 7/13/20 4:30 PM, Nadav Amit wrote: >>> On Jul 13, 2020, at 4:17 PM, Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> wrote: >>> >>> [snip] >>> I am just saying that the APM language "should be cleared to 0" is misleading if the processor doesn't enforce it. >> Just to ensure I am clear - I am not blaming you in any way. I also found >> the phrasing confusing. >> >> Having said that, if you (or anyone else) reintroduces “positive” tests, in >> which the VM CR3 is modified to ensure VM-entry succeeds when the reserved >> non-MBZ bits are set, please ensure the tests fails gracefully. The >> non-long-mode CR3 tests crashed since the VM page-tables were incompatible >> with the paging mode. >> >> In other words, instead of setting a VMMCALL instruction in the VM to trap >> immediately after entry, consider clearing the present-bits in the high >> levels of the NPT; or injecting some exception that would trigger exit >> during vectoring or something like that. >> >> P.S.: If it wasn’t clear, I am not going to fix KVM itself for some obvious >> reasons. > I think since the APM is not clear, re-adding any test that tests those bits, is like adding a test with "undefined behavior" to me. > > > Paolo, Should I send a KVM patch to remove checks for those non-MBZ reserved bits ? Which non-MBZ reserved bits (other than those that I addressed) do you refer to?
