On Wed, Jul 15, 2020 at 11:34:26AM +0200, Joerg Roedel wrote: > 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. Thanks! > > 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. And recursive #VC was instant death, right? Because there's no way to avoid IST stack corruption in that case.
