[xen master] x86/cpu-policy: Simplify logic in guest_common_default_feature_adjustments()

[patchbot@xxxxxxx]

commit 30f8fed68f3c2e63594ff9202b3d05b971781e36
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Jun 27 14:46:01 2025 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Jun 30 12:41:33 2025 +0100

    x86/cpu-policy: Simplify logic in guest_common_default_feature_adjustments()
    
    For features which are unconditionally set in the max policies, making the
    default policy to match the host can be done with a conditional clear.
    
    This is simpler than the unconditional clear, conditional set currently
    performed.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu-policy.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index 060b34d913..518f9c9e54 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -515,17 +515,14 @@ static void __init 
guest_common_default_feature_adjustments(uint32_t *fs)
          * reasons, so reset the default policy back to the host values in
          * case we're unaffected.
          */
-        __clear_bit(X86_FEATURE_MD_CLEAR, fs);
-        if ( cpu_has_md_clear )
-            __set_bit(X86_FEATURE_MD_CLEAR, fs);
+        if ( !cpu_has_md_clear )
+            __clear_bit(X86_FEATURE_MD_CLEAR, fs);
 
-        __clear_bit(X86_FEATURE_FB_CLEAR, fs);
-        if ( cpu_has_fb_clear )
-            __set_bit(X86_FEATURE_FB_CLEAR, fs);
+        if ( !cpu_has_fb_clear )
+            __clear_bit(X86_FEATURE_FB_CLEAR, fs);
 
-        __clear_bit(X86_FEATURE_RFDS_CLEAR, fs);
-        if ( cpu_has_rfds_clear )
-            __set_bit(X86_FEATURE_RFDS_CLEAR, fs);
+        if ( !cpu_has_rfds_clear )
+            __clear_bit(X86_FEATURE_RFDS_CLEAR, fs);
 
         /*
          * The Gather Data Sampling microcode mitigation (August 2023) has an
@@ -545,13 +542,11 @@ static void __init 
guest_common_default_feature_adjustments(uint32_t *fs)
      * Topology information is at the toolstack's discretion so these are
      * unconditionally set in max, but pick a default which matches the host.
      */
-    __clear_bit(X86_FEATURE_HTT, fs);
-    if ( cpu_has_htt )
-        __set_bit(X86_FEATURE_HTT, fs);
+    if ( !cpu_has_htt )
+        __clear_bit(X86_FEATURE_HTT, fs);
 
-    __clear_bit(X86_FEATURE_CMP_LEGACY, fs);
-    if ( cpu_has_cmp_legacy )
-        __set_bit(X86_FEATURE_CMP_LEGACY, fs);
+    if ( !cpu_has_cmp_legacy )
+        __clear_bit(X86_FEATURE_CMP_LEGACY, fs);
 
     /*
      * On certain hardware, speculative or errata workarounds can result in
--
generated by git-patchbot for /home/xen/git/xen.git#master