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The RDPMC-exiting control is dependent on the existence of the RDPMC instruction itself, i.e. is not tied to the "Architectural Performance Monitoring" feature. For all intents and purposes, the control exists on all CPUs with VMX support since RDPMC also exists on all VCPUs with VMX supported. Per Intel's SDM: The RDPMC instruction was introduced into the IA-32 Architecture in the Pentium Pro processor and the Pentium processor with MMX technology. The earlier Pentium processors have performance-monitoring counters, but they must be read with the RDMSR instruction. Because RDPMC-exiting always exists, KVM requires the control and refuses to load if it's not available. As a result, hiding the PMU from a guest breaks nested virtualization if the guest attemts to use KVM. While it's not explicitly stated in the RDPMC pseudocode, the VM-Exit check for RDPMC-exiting follows standard fault vs. VM-Exit prioritization for privileged instructions, e.g. occurs after the CPL/CR0.PE/CR4.PCE checks, but before the counter referenced in ECX is checked for validity. In other words, the original KVM behavior of injecting a #GP was correct, and the KVM unit test needs to be adjusted accordingly, e.g. eat the #GP when the unit test guest (L3 in this case) executes RDPMC without RDPMC-exiting set in the unit test host (L2). This reverts commite51bfdb687. Fixes:e51bfdb687("KVM: nVMX: Expose RDPMC-exiting only when guest supports PMU") Reported-by: David Hill <hilld@binarystorm.net> Cc: Saar Amar <saaramar@microsoft.com> Cc: Mihai Carabas <mihai.carabas@oracle.com> Cc: Jim Mattson <jmattson@google.com> Cc: Liran Alon <liran.alon@oracle.com> Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.