On Fri, Oct 23, 2020 at 10:16 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > On 23/10/20 18:59, Jim Mattson wrote: > >> The problem is that page fault error code bits cannot be reconstructed > >> from bits 0..2 of the EPT violation exit qualification, if bit 8 is > >> clear in the exit qualification (that is, if the access causing the EPT > >> violation is to a paging-structure entry). In that case bits 0..2 refer > >> to the paging-structure access rather than to the final access. In fact > >> advanced information is not available at all for paging-structure access > >> EPT violations. > > > > True, but the in-kernel emulator can only handle a very small subset > > of the available instructions. > > > > If bit 8 is set in the exit qualification, we should use the advanced > > VM-exit information. If it's clear, we should just do a software page > > walk of the guest's x86 page tables. > > The information that we need is _not_ that provided by the advanced > VM-exit information (or by a page walk). If a page is neither writable > nor executable, the advanced information doesn't say if the injected #PF > should be a W=1 or a F=1 fault. We need the information in bits 0..2 of > the exit qualification for the final access, which however is not > available for the paging-structure access. > Are you planning to extend the emulator, then, to support all instructions? I'm not sure where you are going with this.
