Messages in this thread | | | Date | Tue, 3 Mar 2020 14:41:51 -0800 | From | Sean Christopherson <> | Subject | Re: [PATCH 19/61] KVM: VMX: Add helpers to query Intel PT mode |
| |
Disclaimer: I'm going off a few lines in the SDM and the original patches, everything I say could be completely wrong :-)
On Tue, Feb 25, 2020 at 03:54:21PM +0100, Paolo Bonzini wrote: > On 24/02/20 23:18, Sean Christopherson wrote: > >>> { > >>> u32 vmexit_ctrl = vmcs_config.vmexit_ctrl; > >>> - if (pt_mode == PT_MODE_SYSTEM) > >>> + if (vmx_pt_mode_is_system()) > >> ... and here? I.e. to cover the currently unsupported 'host-only' mode. > > Hmm, good question. I don't think so? On VM-Enter, RTIT_CTL would need to > > be loaded to disable PT. Clearing RTIT_CTL on VM-Exit would be redundant > > at that point[1]. And AIUI, the PIP for VM-Enter/VM-Exit isn't needed > > because there is no context switch from the decoder's perspective. > > How does host-only mode differ from "host-guest but don't expose PT to > the guest"? So I would say that host-only mode is a special case of > host-guest, not of system mode.
AIUI, host-guest needs a special packet for VM-Enter/VM-Exit so that the trace analyzer understands there was a context switch. With host-only, the packet isn't needed because tracing stops entirely. So it's not that host-only is a special case of system mode, but rather it doesn't need the VM-Exit control enabled to generate the special packet.
| |