[PATCH 0/3] amd/msr: implement MSR_VIRT_SPEC_CTRL for HVM guests

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Hello,

The following series implements support for MSR_VIRT_SPEC_CTRL on
different AMD CPU families.

Note that the support is added backwards, starting with the newer CPUs
that support MSR_SPEC_CTRL and moving to the older ones either using
MSR_VIRT_SPEC_CTRL or the SSBD bit in LS_CFG.

First patch is quite clean, as it uses the shadow SPEC_CTRL in order to
set the SSBD bit and have it context switched by Xen using the existing
logic recently added.

The next two patches introduce a different way to context switch SSBD
either depending on the underlying SSBD support, so it's either using
VIRT_SPEC_CTRL or the LS_CFG MSR. They also kind of overload the usage of
several spec_ctrl variables in the hypervisor in order to store the
status of SSBD even when not using MSR_SPEC_CTRL itself. I've tried to
document those in the commit messages, but it could be controversial.

Thanks, Roger.

Roger Pau Monne (3):
  amd/msr: implement VIRT_SPEC_CTRL for HVM guests on top of SPEC_CTRL
  amd/msr: allow passthrough of VIRT_SPEC_CTRL for HVM guests
  amd/msr: implement VIRT_SPEC_CTRL for HVM guests using legacy SSBD

 docs/misc/xen-command-line.pandoc           |   5 +-
 xen/arch/x86/cpu/amd.c                      | 116 +++++++++++++++++---
 xen/arch/x86/cpuid.c                        |  18 +++
 xen/arch/x86/hvm/hvm.c                      |   1 +
 xen/arch/x86/hvm/svm/entry.S                |   8 +-
 xen/arch/x86/hvm/svm/svm.c                  |  67 +++++++++++
 xen/arch/x86/include/asm/amd.h              |   3 +
 xen/arch/x86/include/asm/cpufeatures.h      |   2 +
 xen/arch/x86/include/asm/msr.h              |   6 +-
 xen/arch/x86/msr.c                          |  15 +++
 xen/arch/x86/spec_ctrl.c                    |  11 +-
 xen/include/public/arch-x86/cpufeatureset.h |   2 +-
 12 files changed, 230 insertions(+), 24 deletions(-)

-- 
2.34.1