Hardware that exposes SSB_NO can implement the setting of SSBD as a
no-op because it's not affected by SSB.
Take advantage of that and allow exposing VIRT_SPEC_CTRL.SSBD to guest
running on hadrware that has SSB_NO. Only set VIRT_SSBD on the max
policy though, as the feature is only intended to be used for
migration compatibility.
Signed-off-by: Roger Pau Monné <roger....@citrix.com>
---
As there's no hardware with SSB_NO so far the patch is untested. Post
it for reference if there's hardware with the bit set.
---
xen/arch/x86/cpu/amd.c | 4 +++-
xen/arch/x86/cpuid.c | 7 ++++++-
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index cfeb8d1daf..74cfeffc29 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -814,7 +814,9 @@ void amd_set_ssbd(bool enable)
wrmsr(MSR_VIRT_SPEC_CTRL, enable ? SPEC_CTRL_SSBD : 0, 0);
else if ( amd_legacy_ssbd )
core_set_legacy_ssbd(enable);
- else
+ else if ( cpu_has_ssb_no ) {
+ /* Nothing to do. */
+ } else
ASSERT_UNREACHABLE();
}
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index acc2f606ce..e394dbe669 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -558,11 +558,16 @@ static void __init calculate_hvm_max_policy(void)
__clear_bit(X86_FEATURE_IBRSB, hvm_featureset);
__clear_bit(X86_FEATURE_IBRS, hvm_featureset);
}
- else if ( boot_cpu_has(X86_FEATURE_AMD_SSBD) )
+ else if ( boot_cpu_has(X86_FEATURE_AMD_SSBD) ||
+ boot_cpu_has(X86_FEATURE_SSB_NO) )
/*
* If SPEC_CTRL.SSBD is available VIRT_SPEC_CTRL.SSBD can be exposed
* and implemented using the former. Expose in the max policy only as
* the preference is for guests to use SPEC_CTRL.SSBD if available.
+ *
+ * Allow VIRT_SSBD in the max policy if SSB_NO is exposed for migration
+ * compatibility reasons. If SSB_NO is present setting
+ * VIRT_SPEC_CTRL.SSBD is a no-op.
*/
__set_bit(X86_FEATURE_VIRT_SSBD, hvm_featureset);
--
2.37.3
