2017-07-11 16:45-0400, Bandan Das: > Radim Krčmář <rkrcmar@xxxxxxxxxx> writes: > > > 2017-07-11 15:38-0400, Bandan Das: > >> Radim Krčmář <rkrcmar@xxxxxxxxxx> writes: > >> > >> > 2017-07-11 14:35-0400, Bandan Das: > >> >> Jim Mattson <jmattson@xxxxxxxxxx> writes: > >> >> ... > >> >> >>> I can find the definition for an vmexit in case of index >= > >> >> >>> VMFUNC_EPTP_ENTRIES, but not for !vmcs12->eptp_list_address in the SDM. > >> >> >>> > >> >> >>> Can you give me a hint? > >> >> >> > >> >> >> I don't think there is. Since, we are basically emulating eptp switching > >> >> >> for L2, this is a good check to have. > >> >> > > >> >> > There is nothing wrong with a hypervisor using physical page 0 for > >> >> > whatever purpose it likes, including an EPTP list. > >> >> > >> >> Right, but of all the things, a l1 hypervisor wanting page 0 for a eptp list > >> >> address most likely means it forgot to initialize it. Whatever damage it does will > >> >> still end up with vmfunc vmexit anyway. > >> > > >> > Most likely, but not certainly. I also don't see a to diverge from the > >> > spec here. > >> > >> Actually, this is a specific case where I would like to diverge from the spec. > >> But then again, it's L1 shooting itself in the foot and this would be a rarely > >> used code path, so, I am fine removing it. > > > > Thanks, we're not here to judge the guest, but to provide a bare-metal > > experience. :) > > There are certain cases where do. For example, when L2 instruction emulation > fails we decide to kill L2 instead of injecting the error to L1 and let it handle > that. Anyway, that's a different topic, I was just trying to point out there > are cases kvm does a somewhat policy decision... Emulation failure is a KVM bug and we are too lazy to implement the bare-metal behavior correctly, but avoiding the EPTP list bug is actually easier than introducing it. You can make KVM simpler and improve bare-metal emulation at the same time.
