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Intel 64 and IA-32 Architectures Software Developers Manual Volume 3B, System Programming Guide Part 2

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Table Of Contents
Vol. 3 21-21
VMX NON-ROOT OPERATION
causes an APIC-access VM exit). Section 21.5.3 describes the treatment if there is no
APIC-access VM exit and the access is a VTPR access.
21.5.3 VTPR Accesses
As noted in Section 21.2.4, a memory access is a VTPR access if all of the following
hold: (1) the “use TPR shadow” VM-execution control is 1; (2) the access is not for
an instruction fetch; (3) the access is at most 32 bits in width; and (4) the access is
to offset 80H on the APIC-access page.
The treatment of VTPR accesses depends on the nature of the access:
• A linear VTPR access using a translation with a 4-KByte page does not cause an
APIC-access VM exit. Instead, it is converted so that, instead of accessing offset
80H on the APIC-access page, it accesses offset 80H on the virtual-APIC page.
Further details are provided in Section 21.5.3.1 to Section 21.5.3.3.
• A linear VTPR access using a translation with a large page (2-MByte or 4-MByte)
may be treated in either of two ways:
— It may operate on memory on the APIC-access page. The details in Section
21.5.3.1 to Section 21.5.3.3 do not apply.
— It may be converted so that, instead of accessing offset 80H on the APIC-
access page, it accesses offset 80H on the virtual-APIC page. Further details
are provided in Section 21.5.3.1 to Section 21.5.3.3.
• A physical VTPR access may be treated in one of three ways:
— It may cause an APIC-access VM exit. The details in Section 21.5.3.1 to
Section 21.5.3.3 do not apply.
— It may operate on memory on the APIC-access page (and possibly then cause
an APIC-access VM exit). The details in Section 21.5.3.1 to Section 21.5.3.3
do not apply.
— It may be converted so that, instead of accessing offset 80H on the APIC-
access page, it accesses offset 80H on the virtual-APIC page. Further details
are provided in Section 21.5.3.1 to Section 21.5.3.3.
Linear VTPR accesses never cause APIC-access VM exits (recall that an access is a
VTPR access only if the “use TPR shadow” VM-execution control is 1).
21.5.3.1 Treatment of Individual VTPR Accesses
The following items detail the treatment of VTPR accesses:
• VTPR read accesses. Such an access completes normally (reading data from the
field at offset 80H on the virtual-APIC page).
The following items detail certain instructions that are considered to perform
read accesses and how they behavior when accessing the VTPR: