Hello,
The following series implements support for MSR_VIRT_SPEC_CTRL
(VIRT_SSBD) 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.
Xen is still free to use it's own SSBD setting, as the selection is
context switched on vm{entry,exit}.
On Zen2 and later, SPEC_CTRL.SSBD exists and should be used in
preference to VIRT_SPEC_CTRL.SSBD. However, for migration
compatibility, Xen offers VIRT_SSBD to guests (in the max CPUID policy,
not default) implemented in terms of SPEC_CTRL.SSBD.
On Fam15h thru Zen1, Xen exposes VIRT_SSBD to guests by default to
abstract away the model and/or hypervisor specific differences in
MSR_LS_CFG/MSR_VIRT_SPEC_CTRL.
Note that if the hardware itself does offer VIRT_SSBD (ie: very likely
when running virtualized on < Zen2 hardware) and not AMD_SSBD Xen will
allow untrapped access to MSR_VIRT_SPEC_CTRL for HVM guests.
So the implementation of VIRT_SSBD exposed to HVM guests will use one of
the following underlying mechanisms, in the preference order listed
below:
* SPEC_CTRL.SSBD. (patch 1)
* VIRT_SPEC_CTRL.SSBD (untrapped). (patch 2).
* Non-architectural way using LS_CFG. (patch 3)
This has survived a XenRT basic set of tests on AMD machines.
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
xen/arch/x86/cpu/amd.c | 116 +++++++++++++++++---
xen/arch/x86/cpuid.c | 28 +++++
xen/arch/x86/hvm/hvm.c | 1 +
xen/arch/x86/hvm/svm/entry.S | 6 +
xen/arch/x86/hvm/svm/svm.c | 50 +++++++++
xen/arch/x86/include/asm/amd.h | 4 +
xen/arch/x86/include/asm/cpufeatures.h | 1 +
xen/arch/x86/include/asm/msr.h | 14 +++
xen/arch/x86/msr.c | 26 +++++
xen/arch/x86/spec_ctrl.c | 12 +-
xen/include/public/arch-x86/cpufeatureset.h | 2 +-
11 files changed, 241 insertions(+), 19 deletions(-)
--
2.35.1
