On Mon, Jun 26, 2023, Tom Lendacky wrote: > On 6/26/23 11:28, Sean Christopherson wrote: > > On Mon, Jun 26, 2023, Tom Lendacky wrote: > > > On 6/23/23 17:18, Sean Christopherson wrote: > > > > On Fri, Jun 09, 2023, Rick P Edgecombe wrote: > > > > > Also, since the host might have CR4.CET set for its own reasons, if the host > > > > > handled an exit with the the guests MSR_IA32_S_CET set it could suddenly be > > > > > subjected to CET enforcement that it doesn't expect. Waiting to restore it > > > > > until returning to the guest is too late. > > > > > > > > > > At least that's the reasoning on the VMX side as I understand it > > > > > > > > The APM doesn't come right out and say it, but I assume/hope that S_CET is saved > > > > on VMRUN and loaded on #VMEXIT, i.e. is the same as VMX for all intents and > > > > purposes. > > > > > > > > The host save state definitely has a field for S_CET, and VMRUN documents that the > > > > guest values are loaded, I just can't find anything in the APM that explicitly states > > > > how host S_CET and friends are handled. E.g. in theory, they could have been > > > > shoved into VMSAVE+VMLOAD, though I very much doubt that's the case. > > > > > > Yes, the host value is saved/restored on VMRUN/#VMEXIT. Anything that is in > > > the VMCB Save Area (the non-SEV-ES save area) is fully virtualized (unless > > > noted otherwise) and doesn't require special processing to save/restore the > > > host values. > > > > Would it makes sense to add a column in "Table B-2. VMCB Layout, State Save Area" > > to specify whether a field is handled by VMRUN+#VMEXIT vs. VMLOAD+VMSAVE? I can't > > find anywhere in the APM where it explicitly states that VMRUN+#VMEXIT context > > switches everything in the Save Area except the fields listed in "15.5.2 VMSAVE > > and VMLOAD Instructions". > > > > "15.5 VMRUN Instruction" kinda sorta covers that behavior, but the information is > > either incomplete or stale, e.g. for host state it says "at least the following" > > > > Saving Host State. To ensure that the host can resume operation after #VMEXIT, > > VMRUN saves at least the following host state information: > > > > but for guest state it says "the following" > > > > Loading Guest State. After saving host state, VMRUN loads the following guest > > state from the VMCB: > > > > and then both provide incomplete lists of state. A pedantic reading of the guest > > case suggests that there's a large pile of state that *isn't* loaded, and the host > > case isn't all that helpful because it's way too handwavy. > > I'll communicate this feedback to the folks that update the APM volumes and > see what can be done. Thanks, much appreciated!
