On Mon, Jan 13, 2020 at 04:10:50PM +0800, Yang Weijiang wrote: > On Fri, Jan 10, 2020 at 10:04:59AM -0800, Sean Christopherson wrote: > > On Thu, Jan 02, 2020 at 02:13:15PM +0800, Yang Weijiang wrote: > > > @@ -3585,7 +3602,30 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level, > > > if ((error_code & PFERR_WRITE_MASK) && > > > spte_can_locklessly_be_made_writable(spte)) > > > { > > > - new_spte |= PT_WRITABLE_MASK; > > > + /* > > > + * Record write protect fault caused by > > > + * Sub-page Protection, let VMI decide > > > + * the next step. > > > + */ > > > + if (spte & PT_SPP_MASK) { > > > + int len = kvm_x86_ops->get_inst_len(vcpu); > > > > There's got to be a better way to handle SPP exits than adding a helper > > to retrieve the instruction length. > > > The fault instruction was skipped by kvm_skip_emulated_instruction() > before, but Paolo suggested leave the re-do or skip option to user-space > to make it flexible for write protection or write tracking, so return > length to user-space. Sorry, my comment was unclear. I have no objection to punting the fault to userspace, it's the mechanics of how it's done that I dislike. Specifically, (a) using run->exit_reason to propagate the SPP exit up the stack, e.g. instead of modifying affected call stacks to play nice with any exit to userspace, (b) assuming ->get_insn_len() will always be accurate, e.g. see the various caveats in skip_emulated_instruction() for both VMX and SVM, and (c) duplicating the state capture code in every location that can encounter a SPP fault. What I'm hoping is that it's possible to modify the call stacks to explicitly propagate an exit to userspace and/or SPP fault, and shove all the state capture into a common location, e.g. handle_ept_violation(). Side topic, assuming the userspace VMI is going to be instrospecting the faulting instruction, won't it decode the instruction? I.e. calculate the instruction length anyways?