Page 1945

Vol. 3D A-3

VMX CAPABILITY REPORTING FACILITY

A.3.1

Pin-Based VM-Execution Controls

The IA32_VMX_PINBASED_CTLS MSR (index 481H) reports on the allowed settings of most of the pin-based
VM-execution controls (see Section 24.6.1):

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Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the pin-based
VM-execution controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if
control X is 0.
Exceptions are made for the pin-based VM-execution controls in the default1 class (see Appendix A.2). These
are bits 1, 2, and 4; the corresponding bits of the IA32_VMX_PINBASED_CTLS MSR are always read as 1. The
treatment of these controls by VM entry is determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any pin-based VM-execution control in

the default1 class is 0.

— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PINBASED_CTLS MSR (see

below) reports which of the pin-based VM-execution controls in the default1 class can be 0 on VM entry.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in
the MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PINBASED_CTLS MSR (index 48DH)
reports on the allowed settings of all of the pin-based VM-execution controls:

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X to be 0 if bit X in the MSR
is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0. There are no exceptions.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

It is necessary for software to consult only one of the capability MSRs to determine the allowed settings of the pin-
based VM-execution controls:

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 0, all information about the allowed settings of the pin-based
VM-execution controls is contained in the IA32_VMX_PINBASED_CTLS MSR. (The
IA32_VMX_TRUE_PINBASED_CTLS MSR is not supported.)

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, all information about the allowed settings of the pin-based
VM-execution controls is contained in the IA32_VMX_TRUE_PINBASED_CTLS MSR. Assuming that software
knows that the default1 class of pin-based VM-execution controls contains bits 1, 2, and 4, there is no need for
software to consult the IA32_VMX_PINBASED_CTLS MSR.

A.3.2

Primary Processor-Based VM-Execution Controls

The IA32_VMX_PROCBASED_CTLS MSR (index 482H) reports on the allowed settings of most of the primary
processor-based VM-execution controls (see Section 24.6.2):

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the primary
processor-based VM-execution controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to
1, VM entry fails if control X is 0.
Exceptions are made for the primary processor-based VM-execution controls in the default1 class (see
Appendix A.2). These are bits 1, 4–6, 8, 13–16, and 26; the corresponding bits of the
IA32_VMX_PROCBASED_CTLS MSR are always read as 1. The treatment of these controls by VM entry is
determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any of the primary processor-based VM-

execution controls in the default1 class is 0.

— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PROCBASED_CTLS MSR (see

below) reports which of the primary processor-based VM-execution controls in the default1 class can be 0
on VM entry.

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