[PATCH v4 0/2] x86: Add the feature Virtual SPEC_CTRL

[Babu Moger]

Newer AMD processors have a feature to virtualize the use of the
SPEC_CTRL MSR on the guest. The series adds the feature support
and enables the feature on SVM.
---
v4:
  1. Taken care of comments from Sean Christopherson.
     a. Updated svm_set_msr/svm_get_msr to read/write the spec_ctrl value
        directly from save spec_ctrl.
     b. Disabled the msr_interception in init_vmcb when V_SPEC_CTRL is
        present.
     c. Added the save restore for nested vm. Also tested to make sure
        the nested SPEC_CTRL settings properly saved and restored between
        L2 and L1 guests.
  2. Added the kvm-unit-tests to verify that. Sent those patches separately.

v3:
  1. Taken care of recent changes in vmcb_save_area. Needed to adjust the save
     area spec_ctrl definition.
  2. Taken care of few comments from Tom.
     a. Initialised the save area spec_ctrl in case of SEV-ES.
     b. Removed the changes in svm_get_msr/svm_set_msr.
     c. Reverted the changes to disable the msr interception to avoid compatibility
        issue.
  3. Updated the patch #1 with Acked-by from Boris.
  
v2:
  NOTE: This is not final yet. Sending out the patches to make
  sure I captured all the comments correctly.

  1. Most of the changes are related to Jim and Sean's feedback.
  2. Improved the description of patch #2.
  3. Updated the vmcb save area's guest spec_ctrl value(offset 0x2E0)
     properly. Initialized during init_vmcb and svm_set_msr and
     returned the value from save area for svm_get_msr.
  4. As Jim commented, transferred the value into the VMCB prior
     to VMRUN and out of the VMCB after #VMEXIT.
  5. Added kvm-unit-test to detect the SPEC CTRL feature.
     https://lore.kernel.org/kvm/160865324865.19910.5159218511905134908.stgit@bmoger-ubuntu/
  6. Sean mantioned of renaming MSR_AMD64_VIRT_SPEC_CTRL. But, it might
     create even more confusion, so dropped the idea for now.

v3: https://lore.kernel.org/kvm/161073115461.13848.18035972823733547803.stgit@bmoger-ubuntu/
v2: https://lore.kernel.org/kvm/160867624053.3471.7106539070175910424.stgit@bmoger-ubuntu/
v1: https://lore.kernel.org/kvm/160738054169.28590.5171339079028237631.stgit@bmoger-ubuntu/

Babu Moger (2):
      x86/cpufeatures: Add the Virtual SPEC_CTRL feature
      KVM: SVM: Add support for Virtual SPEC_CTRL


 arch/x86/include/asm/cpufeatures.h |    1 +
 arch/x86/include/asm/svm.h         |    4 +++-
 arch/x86/kvm/svm/nested.c          |    2 ++
 arch/x86/kvm/svm/svm.c             |   27 ++++++++++++++++++++++-----
 4 files changed, 28 insertions(+), 6 deletions(-)

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