[v4,0/4] Restrict PV features to only enabled guests

Message

Oliver Upton Aug. 18, 2020, 3:24 p.m. UTC

To date, KVM has allowed guests to use paravirtual interfaces regardless
of the configured CPUID. While almost any guest will consult the
KVM_CPUID_FEATURES leaf _before_ using PV features, it is still
undesirable to have such interfaces silently present.

This series aims to address the issue by adding explicit checks against
the guest's CPUID when servicing any paravirtual feature. Since this
effectively changes the guest/hypervisor ABI, a KVM_CAP is warranted to
guard the new behavior.

Patches 1-2 refactor some of the PV code in anticipation of the change.
Patch 3 introduces the checks + KVM_CAP. Finally, patch 4 fixes some doc
typos that were noticed when working on this series.

v1 => v2:
 - Strip Change-Id footers (checkpatch is your friend!)

v2 => v3:
 - Mark kvm_write_system_time() as static

v3 => v4:
 - Address Wanpeng's concerns regarding cpuid lookup

Parent commit: e792415c5d3e ("KVM: MIPS/VZ: Fix build error caused by 'kvm_run' cleanup")

Oliver Upton (4):
  kvm: x86: encapsulate wrmsr(MSR_KVM_SYSTEM_TIME) emulation in helper
    fn
  kvm: x86: set wall_clock in kvm_write_wall_clock()
  kvm: x86: only provide PV features if enabled in guest's CPUID
  Documentation: kvm: fix some typos in cpuid.rst

 Documentation/virt/kvm/api.rst   |  11 +++
 Documentation/virt/kvm/cpuid.rst |  88 +++++++++++-----------
 arch/x86/include/asm/kvm_host.h  |  15 ++++
 arch/x86/kvm/cpuid.c             |   7 ++
 arch/x86/kvm/cpuid.h             |  10 +++
 arch/x86/kvm/x86.c               | 122 +++++++++++++++++++++++--------
 include/uapi/linux/kvm.h         |   1 +
 7 files changed, 181 insertions(+), 73 deletions(-)