On Fri, Aug 28, 2020 at 5:57 PM Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> wrote: > > If the P (present) bit in an NPT entry is cleared, VMRUN will fail and the > guest will exit to the host with an exit code of 0x400 (#NPF). The following > bits of importance in EXITINFO1 will be set/cleared to indicate the failure: > > bit# 0: cleared > bit# 32: set This seems like a terrible commit description. First, the P bit can be cleared in a plethora of NPT entries without having any effect on guest execution. It's only if the guest tries to access a GPA whose translation uses the non-present NPT entry that there is an issue. Second, the VMRUN does not fail. If the VM-exit code is anything other than -1, the VMRUN has succeeded. Third, the bits in EXITINFO that get set/cleared depend very much on the actual access. Yes, if the nested page walk terminates due to a non-present page, bit 0 will be cleared. However, bit 32 will only be set if the non-present page was encountered while translating the final guest physical address (not the guest physical address of a page table page encountered during the walk). Moreover, older AMD hardware never sets bits 32 or 33 at all. Bit 1 will be set if the access was a write (or a page table walk). Bit 2 will be set for a user access. Bit 4 will be set for a code read (while translating the final guest physical address).
