[xen stable-4.16] x86/spec-ctrl: Introduce new has_spec_ctrl boolean

[patchbot@xxxxxxx]

commit 08fc03c855c071e9b1aaaa96403f2a90433336a7
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jan 25 17:14:48 2022 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Feb 4 15:45:25 2022 +0000

    x86/spec-ctrl: Introduce new has_spec_ctrl boolean
    
    Most MSR_SPEC_CTRL setup will be common between Intel and AMD.  Instead of
    opencoding an OR of two features everywhere, introduce has_spec_ctrl 
instead.
    
    Reword the comment above the Intel specific alternatives block to highlight
    that it is Intel specific, and pull the setting of 
default_xen_spec_ctrl.IBRS
    out because it will want to be common.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 5d9eff3a312763d889cfbf3c8468b6dfb3ab490c)
---
 xen/arch/x86/spec_ctrl.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 8a550d0a09..2072daf662 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 ibrs = false, hw_smt_enabled;
+    bool has_spec_ctrl, ibrs = false, hw_smt_enabled;
     bool cpu_has_bug_taa;
     uint64_t caps = 0;
 
@@ -936,6 +936,8 @@ void __init init_speculation_mitigations(void)
 
     hw_smt_enabled = check_smt_enabled();
 
+    has_spec_ctrl = boot_cpu_has(X86_FEATURE_IBRSB);
+
     /*
      * First, disable the use of retpolines if Xen is using shadow stacks, as
      * they are incompatible.
@@ -973,11 +975,11 @@ void __init init_speculation_mitigations(void)
              */
             else if ( retpoline_safe(caps) )
                 thunk = THUNK_RETPOLINE;
-            else if ( boot_cpu_has(X86_FEATURE_IBRSB) )
+            else if ( has_spec_ctrl )
                 ibrs = true;
         }
         /* Without compiler thunk support, use IBRS if available. */
-        else if ( boot_cpu_has(X86_FEATURE_IBRSB) )
+        else if ( has_spec_ctrl )
             ibrs = true;
     }
 
@@ -1008,10 +1010,7 @@ void __init init_speculation_mitigations(void)
     else if ( thunk == THUNK_JMP )
         setup_force_cpu_cap(X86_FEATURE_IND_THUNK_JMP);
 
-    /*
-     * If we are on hardware supporting MSR_SPEC_CTRL, see about setting up
-     * the alternatives blocks so we can virtualise support for guests.
-     */
+    /* Intel hardware: MSR_SPEC_CTRL alternatives setup. */
     if ( boot_cpu_has(X86_FEATURE_IBRSB) )
     {
         if ( opt_msr_sc_pv )
@@ -1030,11 +1029,12 @@ void __init init_speculation_mitigations(void)
             default_spec_ctrl_flags |= SCF_ist_wrmsr;
             setup_force_cpu_cap(X86_FEATURE_SC_MSR_HVM);
         }
-
-        if ( ibrs )
-            default_xen_spec_ctrl |= SPEC_CTRL_IBRS;
     }
 
+    /* If we have IBRS available, see whether we should use it. */
+    if ( has_spec_ctrl && ibrs )
+        default_xen_spec_ctrl |= SPEC_CTRL_IBRS;
+
     /* If we have SSBD available, see whether we should use it. */
     if ( boot_cpu_has(X86_FEATURE_SSBD) && opt_ssbd )
         default_xen_spec_ctrl |= SPEC_CTRL_SSBD;
@@ -1268,7 +1268,7 @@ void __init init_speculation_mitigations(void)
      * boot won't have any other code running in a position to mount an
      * attack.
      */
-    if ( boot_cpu_has(X86_FEATURE_IBRSB) )
+    if ( has_spec_ctrl )
     {
         bsp_delay_spec_ctrl = !cpu_has_hypervisor && default_xen_spec_ctrl;
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16