Update README.md

README.md

@@ -10,5 +10,11 @@ This project uses WDK and thus Windows Kernel functions to facilitate vmxlaunch.
 
 ### VMCS
 
+This section of the readme just contains note and a list of things i stumbled on and took me a while to figure out and fix.
+
+### VMCS Controls
+
+* One of the mistakes I made early on was setting bits high after applying high/low MSR values. For example my xeons dont support Intel Processor Trace (Intel PT) and I was setting `entry_ctls.conceal_vmx_from_pt = true` after applying the MSR high/low masks. This caused vmxerror #7 (invalid vmcs controls). Now i set the bit high before i apply the high/low bit mask so if my hypervisor runs on a cpu that has Intel PT support it will be concealed from Intel PT.
+
 Dump of VMCS control fields can be found [here](https://githacks.org/_xeroxz/bluepill/-/blob/master/VMCS.md). This is not required, but for learning its nice to
 see exactly what the MSR masks are, and what VMCS field's are enabled after you apply high/low bit masks.