On Wed, Jul 15, 2020 at 11:24:56AM +0200, Peter Zijlstra wrote: > Can we get some more words -- preferably in actual code comments, on > when exactly #VC happens? Sure, will add this as a comment before the actual runtime VC handler. > Because the only thing I remember is that #VC could happen on any memop, > but I also have vague memories of that being a later extention. Currently it is only raised when something happens that the hypervisor intercepts, for example on a couple of instructions like CPUID, RD/WRMSR, ..., or on MMIO/IOIO accesses. With Secure Nested Paging (SNP), which needs additional enablement, a #VC can happen on any memory access. I wrote the IST handling entry code for #VC with that in mind, but do not actually enable it. This is the reason why the #VC handler just panics the system when it ends up on the fall-back (VC2) stack, with SNP enabled it needs to handle the SNP exit-codes in that path. Regards, Joerg
