On Mon, Apr 27, 2020 at 10:37:41AM -0700, Andy Lutomirski wrote: > I have a somewhat serious question: should we use IST for #VC at all? > As I understand it, Rome and Naples make it mandatory for hypervisors > to intercept #DB, which means that, due to the MOV SS mess, it's sort > of mandatory to use IST for #VC. But Milan fixes the #DB issue, so, > if we're running under a sufficiently sensible hypervisor, we don't > need IST for #VC. The reason for #VC being IST is not only #DB, but also SEV-SNP. SNP adds page ownership tracking between guest and host, so that the hypervisor can't remap guest pages without the guest noticing. If there is a violation of ownership, which can happen at any memory access, there will be a #VC exception to notify the guest. And as this can happen anywhere, for example on a carefully crafted stack page set by userspace before doing SYSCALL, the only robust choice for #VC is to use IST. Regards, Joerg
