[Xen-devel] [PATCH v2] xc_cpuid_x86.c: Simplify masking conditions and remove redundant work

[Zhuo Song <alfred.z.song@xxxxxxxxx>]

* Since there would not be 32-bit hypervisor, we do not need
  hypervisor_is_64bit() again.

* Remove xen_64bit from xc_cpuid_pv_policy().

* Move conditionals for LM/NX masking into architectural logic.

* Since RDTSCP could be used for both 64-bit and 32-bit architectures,
  we do not need the tying to 64-bit in intel_xc_cpuid_policy().

* vmx_cpuid_intercept() has covered SYSCALL masking when vmexit and
  original is_64bit or is_pae could not cover whether guest OS is really
  in long mode or not. Here to drop the conditionals and leave it to
  vmexit handler to do the real work.

Signed-off-by: Zhuo Song <songzhuo.sz@xxxxxxxxxxxxxxx>
---
 tools/libxc/xc_cpuid_x86.c | 40 ++++++++++++++++------------------------
 1 file changed, 16 insertions(+), 24 deletions(-)

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index 6b81641..a022202 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -34,13 +34,6 @@
 #define DEF_MAX_INTELEXT  0x80000008u
 #define DEF_MAX_AMDEXT    0x8000001cu
 
-static int hypervisor_is_64bit(xc_interface *xch)
-{
-    xen_capabilities_info_t xen_caps = "";
-    return ((xc_version(xch, XENVER_capabilities, &xen_caps) == 0) &&
-            (strstr(xen_caps, "x86_64") != NULL));
-}
-
 static void cpuid(const unsigned int *input, unsigned int *regs)
 {
     unsigned int count = (input[1] == XEN_CPUID_INPUT_UNUSED) ? 0 : input[1];
@@ -95,13 +88,11 @@ static void amd_xc_cpuid_policy(
         break;
 
     case 0x80000001: {
-        int is_64bit = hypervisor_is_64bit(xch) && is_pae;
-
         if ( !is_pae )
             clear_bit(X86_FEATURE_PAE, regs[3]);
 
         /* Filter all other features according to a whitelist. */
-        regs[2] &= ((is_64bit ? bitmaskof(X86_FEATURE_LAHF_LM) : 0) |
+        regs[2] &= (bitmaskof(X86_FEATURE_LAHF_LM) |
                     bitmaskof(X86_FEATURE_CMP_LEGACY) |
                     (is_nestedhvm ? bitmaskof(X86_FEATURE_SVM) : 0) |
                     bitmaskof(X86_FEATURE_CR8_LEGACY) |
@@ -116,8 +107,8 @@ static void amd_xc_cpuid_policy(
                     bitmaskof(X86_FEATURE_TBM) |
                     bitmaskof(X86_FEATURE_DBEXT));
         regs[3] &= (0x0183f3ff | /* features shared with 0x00000001:EDX */
-                    (is_pae ? bitmaskof(X86_FEATURE_NX) : 0) |
-                    (is_64bit ? bitmaskof(X86_FEATURE_LM) : 0) |
+                    bitmaskof(X86_FEATURE_NX) |
+                    bitmaskof(X86_FEATURE_LM) |
                     bitmaskof(X86_FEATURE_SYSCALL) |
                     bitmaskof(X86_FEATURE_MP) |
                     bitmaskof(X86_FEATURE_MMXEXT) |
@@ -195,16 +186,14 @@ static void intel_xc_cpuid_policy(
         break;
 
     case 0x80000001: {
-        int is_64bit = hypervisor_is_64bit(xch) && is_pae;
-
         /* Only a few features are advertised in Intel's 0x80000001. */
-        regs[2] &= (is_64bit ? bitmaskof(X86_FEATURE_LAHF_LM) : 0) |
-                               bitmaskof(X86_FEATURE_3DNOWPREFETCH) |
-                               bitmaskof(X86_FEATURE_ABM);
-        regs[3] &= ((is_pae ? bitmaskof(X86_FEATURE_NX) : 0) |
-                    (is_64bit ? bitmaskof(X86_FEATURE_LM) : 0) |
-                    (is_64bit ? bitmaskof(X86_FEATURE_SYSCALL) : 0) |
-                    (is_64bit ? bitmaskof(X86_FEATURE_RDTSCP) : 0));
+        regs[2] &= (bitmaskof(X86_FEATURE_LAHF_LM) |
+                    bitmaskof(X86_FEATURE_3DNOWPREFETCH) |
+                    bitmaskof(X86_FEATURE_ABM);
+        regs[3] &= (bitmaskof(X86_FEATURE_NX) |
+                    bitmaskof(X86_FEATURE_LM) |
+                    bitmaskof(X86_FEATURE_SYSCALL) |
+                    bitmaskof(X86_FEATURE_RDTSCP));
         break;
     }
 
@@ -391,7 +380,10 @@ static void xc_cpuid_hvm_policy(
         break;
 
     case 0x80000001:
-        if ( !is_pae ) {
+        if ( !is_pae )
+        {
+            clear_bit(X86_FEATURE_LAHF_LM, regs[2]);
+            clear_bit(X86_FEATURE_LM, regs[3]);
             clear_bit(X86_FEATURE_NX, regs[3]);
             clear_bit(X86_FEATURE_PSE36, regs[3]);
         }
@@ -442,7 +434,7 @@ static void xc_cpuid_pv_policy(
 {
     DECLARE_DOMCTL;
     unsigned int guest_width;
-    int guest_64bit, xen_64bit = hypervisor_is_64bit(xch);
+    int guest_64bit;
     char brand[13];
     uint64_t xfeature_mask;
 
@@ -474,7 +466,7 @@ static void xc_cpuid_pv_policy(
     switch ( input[0] )
     {
     case 0x00000001:
-        if ( !xen_64bit || strstr(brand, "AMD") )
+        if ( strstr(brand, "AMD") )
             clear_bit(X86_FEATURE_SEP, regs[3]);
         clear_bit(X86_FEATURE_DS, regs[3]);
         clear_bit(X86_FEATURE_ACC, regs[3]);
-- 
1.8.5.2 (Apple Git-48)


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