Several bugfixes have reduced the utility of this variable from it's original purpose, and now all it does is aid in the setup of SCF_ist_wrmsr.
Simplify the logic by drop the variable, and doubling up the setting of SCF_ist_wrmsr for the PV and HVM blocks, which will make the AMD SPEC_CTRL support easier to follow. Leave a comment explaining why SCF_ist_wrmsr is still necessary for the VMExit case. No functional change. Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> Reviewed-by: Jan Beulich <jbeul...@suse.com> --- CC: Jan Beulich <jbeul...@suse.com> CC: Roger Pau Monné <roger....@citrix.com> CC: Wei Liu <w...@xen.org> --- xen/arch/x86/spec_ctrl.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c index c18cc8aa493a..8a550d0a0902 100644 --- a/xen/arch/x86/spec_ctrl.c +++ b/xen/arch/x86/spec_ctrl.c @@ -927,7 +927,7 @@ static __init void mds_calculations(uint64_t caps) void __init init_speculation_mitigations(void) { enum ind_thunk thunk = THUNK_DEFAULT; - bool use_spec_ctrl = false, ibrs = false, hw_smt_enabled; + bool ibrs = false, hw_smt_enabled; bool cpu_has_bug_taa; uint64_t caps = 0; @@ -1016,19 +1016,21 @@ void __init init_speculation_mitigations(void) { if ( opt_msr_sc_pv ) { - use_spec_ctrl = true; + default_spec_ctrl_flags |= SCF_ist_wrmsr; setup_force_cpu_cap(X86_FEATURE_SC_MSR_PV); } if ( opt_msr_sc_hvm ) { - use_spec_ctrl = true; + /* + * While the guest MSR_SPEC_CTRL value is loaded/saved atomically, + * Xen's value is not restored atomically. An early NMI hitting + * the VMExit path needs to restore Xen's value for safety. + */ + default_spec_ctrl_flags |= SCF_ist_wrmsr; setup_force_cpu_cap(X86_FEATURE_SC_MSR_HVM); } - if ( use_spec_ctrl ) - default_spec_ctrl_flags |= SCF_ist_wrmsr; - if ( ibrs ) default_xen_spec_ctrl |= SPEC_CTRL_IBRS; } -- 2.11.0