[Bug 54461] New: nVMX: Downgrading nested VMX features from user-space

* [Bug 54461] New: nVMX: Downgrading nested VMX features from user-space
@ 2013-02-25 13:50 bugzilla-daemon
  2013-02-25 13:51 ` [Bug 54461] " bugzilla-daemon
  2015-03-17  3:53 ` bugzilla-daemon
  0 siblings, 2 replies; 3+ messages in thread
From: bugzilla-daemon @ 2013-02-25 13:50 UTC (permalink / raw)
  To: kvm

https://bugzilla.kernel.org/show_bug.cgi?id=54461

           Summary: nVMX: Downgrading nested VMX features from user-space
           Product: Virtualization
           Version: unspecified
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: kvm
        AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
        ReportedBy: nyh@math.technion.ac.il
        Regression: No

In nested SVM, the sub-features of SVM are all part of CPUID, so we already
have a user-space interface (KVM_GET_SUPPORTED_CPUID/KVM_SET_CPUID2) to set a
guest's features - which is, for example, useful for dictating a fixed set of
features across different hosts.

However, in nested VMX, the VMX sub-features offered or not to the guest are
not in CPUID, but rather in MSRs, and currently the
nested_vmx_setup_ctls_msrs() function determines their value - without any
option for user space to control this. We need some sort of new
KVM_SET_READONLY_MSRS ioctl for overriding  (downgrading)
nested_vmx_setup_ctls_msrs()'s decisions for a particular guest.

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