From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Tue, 25 Jan 2022 16:09:59 +0000 (+0000)
Subject: x86/spec-ctrl: Drop use_spec_ctrl boolean
X-Git-Url: http://xenbits.xenproject.org/gitweb/?p=xen.git;a=commitdiff_plain;h=35d0ea6726f8f013cbf3699a90309136896ae55e
x86/spec-ctrl: Drop use_spec_ctrl boolean
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.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit ec083bf552c35e10347449e21809f4780f8155d2)
---
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index f70535b6e7..e85b0c0c7d 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -898,7 +898,7 @@ 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;
@@ -987,19 +987,21 @@ 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;
}