[Bug 216091] KVM nested virtualization does not support VMX fields that should always be supported

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=216091

Sean Christopherson (seanjc@google.com) changed:

           What    |Removed                     |Added
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                 CC|                            |seanjc@google.com

--- Comment #1 from Sean Christopherson (seanjc@google.com) ---
The CR3-target values are clear cut, "A.6 MISCELLANEOUS DATA" in the SDM
explicitly calls out '0' as a legal value for the number of CR3-target values:

  Bits 24:16 indicate the number of CR3-target values supported by the
processor.
  This number is a value between 0 and 256, inclusive (bit 24 is set if and
only
  if bits 23:16 are clear).

For the other fields ("Executive-VMCS pointer", "Guest SMBASE", and "I/O R*X",
I would argue that the lack of a footnote is an SDM bug, as those fields should
exist if and only if the CPU enumerates support for an SMM-transfer monitor in
MSR_IA32_VMX_BASIC, and KVM never sets that bit (49).  The I/O fields "are used
only for VM exits due to SMIs ...", and SMIs are not true VM-Exits when not
using STM.

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