[xen stable-4.18] x86/spec: adjust logic that elides lfence

[patchbot@xxxxxxx]

commit f0ff1d9cb96041a84a24857a6464628240deed4f
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Apr 29 09:37:29 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Apr 29 09:37:29 2024 +0200

    x86/spec: adjust logic that elides lfence
    
    It's currently too restrictive by just checking whether there's a BHB 
clearing
    sequence selected.  It should instead check whether BHB clearing is used on
    entry from PV or HVM specifically.
    
    Switch to use opt_bhb_entry_{pv,hvm} instead, and then remove 
cpu_has_bhb_seq
    since it no longer has any users.
    
    Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
    Fixes: 954c983abcee ('x86/spec-ctrl: Software BHB-clearing sequences')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 656ae8f1091bcefec9c46ec3ea3ac2118742d4f6
    master date: 2024-04-25 16:37:01 +0200
---
 xen/arch/x86/include/asm/cpufeature.h | 3 ---
 xen/arch/x86/spec_ctrl.c              | 6 +++---
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index 7a312c485e..3c57f55de0 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -228,9 +228,6 @@ static inline bool boot_cpu_has(unsigned int feat)
 #define cpu_bug_fpu_ptrs        boot_cpu_has(X86_BUG_FPU_PTRS)
 #define cpu_bug_null_seg        boot_cpu_has(X86_BUG_NULL_SEG)
 
-#define cpu_has_bhb_seq        (boot_cpu_has(X86_SPEC_BHB_TSX) ||       \
-                                boot_cpu_has(X86_SPEC_BHB_LOOPS))
-
 enum _cache_type {
     CACHE_TYPE_NULL = 0,
     CACHE_TYPE_DATA = 1,
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 8c67d6256a..12c19b7eca 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -2328,7 +2328,7 @@ void __init init_speculation_mitigations(void)
          * unconditional WRMSR.  If we do have it, or we're not using any
          * prior conditional block, then it's safe to drop the LFENCE.
          */
-        if ( !cpu_has_bhb_seq &&
+        if ( !opt_bhb_entry_pv &&
              (boot_cpu_has(X86_FEATURE_SC_MSR_PV) ||
               !boot_cpu_has(X86_FEATURE_IBPB_ENTRY_PV)) )
             setup_force_cpu_cap(X86_SPEC_NO_LFENCE_ENTRY_PV);
@@ -2344,7 +2344,7 @@ void __init init_speculation_mitigations(void)
          * active in the block that is skipped when interrupting guest
          * context, then it's safe to drop the LFENCE.
          */
-        if ( !cpu_has_bhb_seq &&
+        if ( !opt_bhb_entry_pv &&
              (boot_cpu_has(X86_FEATURE_SC_MSR_PV) ||
               (!boot_cpu_has(X86_FEATURE_IBPB_ENTRY_PV) &&
                !boot_cpu_has(X86_FEATURE_SC_RSB_PV))) )
@@ -2356,7 +2356,7 @@ void __init init_speculation_mitigations(void)
          * A BHB sequence, if used, is the only conditional action, so if we
          * don't have it, we don't need the safety LFENCE.
          */
-        if ( !cpu_has_bhb_seq )
+        if ( !opt_bhb_entry_hvm )
             setup_force_cpu_cap(X86_SPEC_NO_LFENCE_ENTRY_VMX);
     }
 
--
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