On 9/16/20 11:49 AM, Sean Christopherson wrote: > On Wed, Sep 16, 2020 at 11:38:38AM -0500, Tom Lendacky wrote: >> >> >> On 9/16/20 11:02 AM, Sean Christopherson wrote: >>> On Wed, Sep 16, 2020 at 10:11:10AM -0500, Tom Lendacky wrote: >>>> On 9/15/20 3:13 PM, Tom Lendacky wrote: >>>>> On 9/15/20 11:30 AM, Sean Christopherson wrote: >>>>>> I don't quite follow the "doesn't mean debugging can't be done in the future". >>>>>> Does that imply that debugging could be supported for SEV-ES guests, even if >>>>>> they have an encrypted VMSA? >>>>> >>>>> Almost anything can be done with software. It would require a lot of >>>>> hypervisor and guest code and changes to the GHCB spec, etc. So given >>>>> that, probably just the check for arch.guest_state_protected is enough for >>>>> now. I'll just need to be sure none of the debugging paths can be taken >>>>> before the VMSA is encrypted. >>>> >>>> So I don't think there's any guarantee that the KVM_SET_GUEST_DEBUG ioctl >>>> couldn't be called before the VMSA is encrypted, meaning I can't check the >>>> arch.guest_state_protected bit for that call. So if we really want to get >>>> rid of the allow_debug() op, I'd need some other way to indicate that this >>>> is an SEV-ES / protected state guest. >>> >>> Would anything break if KVM "speculatively" set guest_state_protected before >>> LAUNCH_UPDATE_VMSA? E.g. does KVM need to emulate before LAUNCH_UPDATE_VMSA? >> >> Yes, the way the code is set up, the guest state (VMSA) is initialized in >> the same way it is today (mostly) and that state is encrypted by the >> LAUNCH_UPDATE_VMSA call. I check the guest_state_protected bit to decide >> on whether to direct the updates to the real VMSA (before it's encrypted) >> or the GHCB (that's the get_vmsa() function from patch #5). > > Ah, gotcha. Would it work to set guest_state_protected[*] from time zero, > and move vmsa_encrypted to struct vcpu_svm? I.e. keep vmsa_encrypted, but > use it only for guiding get_vmsa() and related behavior. It is mainly __set_sregs() that needs to know when to allow the register writes and when not to. During guest initialization, __set_sregs is how some of the VMSA is initialized by Qemu. Thanks, Tom >
