Bug 267023

Summary:	bhyve subtly broken on VT-x without exit-on-hlt
Product:	Base System	Reporter:	John Baldwin <jhb>
Component:	bhyve	Assignee:	freebsd-virtualization (Nobody) <virtualization>
Status:	New ---
Severity:	Affects Only Me	CC:	emaste
Priority:	---
Version:	CURRENT
Hardware:	Any
OS:	Any

Description John Baldwin freebsd_committer

2022-10-13 16:54:24 UTC

The VMCS contains a field that is set to 1 to indicate that there is a pending HLT.  In this state, vmxrun will still HLT on resume even if, e.g., the RIP has been updated to point to a different instruction.  VMMs are required to explicitly clear this field after a VMexit due to a HLT if the processor should resume.

See also: https://www.illumos.org/issues/15079

Comment 1 John Baldwin freebsd_committer

2022-10-13 16:56:26 UTC

I got the sense backwards in my description.  VM exits due to HLT are fine, it's when the vCPU exits for some other reason while HLTed that the field in the VMCS is set and needs to be reset before resuming.