[v2,0/3] Add Automatic IBRS support

Message

Alejandro Vallejo May 30, 2023, 1:58 p.m. UTC

v2:
  * Renamed AUTOMATIC to AUTO
  * Style change in xen-cpuid.c
  * Swapped patches 2 and 3
  * Modified trampoline_efer from the BSP so APs use it during boot and S3
    wakeups pick it up.
  * Avoid the delay setting AutoIBRS

Adds support for AMD's Automatic IBRS. It's a set-and-forget feature that
prevents lower privileged executions from affecting speculations of higher
privileged executions, so retpolines are not required. Furthermore, it
clears the RSB upon VMEXIT, so we can avoid doing it if the feature is
present.

Patch 1 adds the relevant bit definitions for CPUID and EFER.

Patch 2 exposes the feature to HVM guests.

Patch 3 Hooks up AutoIBRS to spec_ctrl. so it's used when IBRS is picked.
        It also tweaks the heuristics so AutoIBRS is preferred over
        retpolines as BTI mitigation. This is enough to protect Xen.

Alejandro Vallejo (3):
  x86: Add bit definitions for Automatic IBRS
  x86: Expose Automatic IBRS to guests
  x86: Add support for AMD's Automatic IBRS

 tools/libs/light/libxl_cpuid.c              |  1 +
 tools/misc/xen-cpuid.c                      |  1 +
 xen/arch/x86/hvm/hvm.c                      |  3 ++
 xen/arch/x86/include/asm/cpufeature.h       |  1 +
 xen/arch/x86/include/asm/msr-index.h        |  4 +-
 xen/arch/x86/pv/emul-priv-op.c              |  4 +-
 xen/arch/x86/spec_ctrl.c                    | 45 ++++++++++++++++-----
 xen/include/public/arch-x86/cpufeatureset.h |  1 +
 8 files changed, 46 insertions(+), 14 deletions(-)