[Xen-devel] [PATCH] x86/svm: Improve code generation from cpu_has_svm_feature()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Taking svm_feature_flags by pointer and using test_bit() results in generated
code which loads svm_feature_flags into a 32bit register, then does a bitwise
operation.

The logic can be expressed in terms of a straight bitwise operation, resulting
in the following minor improvement.

  add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-136 (-136)
  Function                                     old     new   delta
  svm_nested_features_on_efer_update           281     273      -8
  svm_create_vmcb                             1404    1388     -16
  svm_vmexit_handler                          6271    6239     -32
  start_svm                                    818     738     -80
  Total: Before=3347569, After=3347433, chg -0.00%

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
CC: Brian Woods <brian.woods@xxxxxxx>
---
 xen/include/asm-x86/hvm/svm/svm.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/xen/include/asm-x86/hvm/svm/svm.h 
b/xen/include/asm-x86/hvm/svm/svm.h
index 49dca39..6e688a8 100644
--- a/xen/include/asm-x86/hvm/svm/svm.h
+++ b/xen/include/asm-x86/hvm/svm/svm.h
@@ -21,7 +21,6 @@
 #define __ASM_X86_HVM_SVM_H__
 
 #include <xen/types.h>
-#include <xen/bitmap.h>
 
 #define svm_vmload(x)     svm_vmload_pa(__pa(x))
 #define svm_vmsave(x)     svm_vmsave_pa(__pa(x))
@@ -77,7 +76,7 @@ extern u32 svm_feature_flags;
 #define SVM_FEATURE_VLOADSAVE     15 /* virtual vmload/vmsave */
 #define SVM_FEATURE_VGIF          16 /* Virtual GIF */
 
-#define cpu_has_svm_feature(f) test_bit(f, &svm_feature_flags)
+#define cpu_has_svm_feature(f) (svm_feature_flags & (1u << (f)))
 #define cpu_has_svm_npt       cpu_has_svm_feature(SVM_FEATURE_NPT)
 #define cpu_has_svm_lbrv      cpu_has_svm_feature(SVM_FEATURE_LBRV)
 #define cpu_has_svm_svml      cpu_has_svm_feature(SVM_FEATURE_SVML)
-- 
2.1.4


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