[Xen-devel] [PATCH] hide RDTSCP feature flag from PV guests

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

Linux 2.6.19 (x86-64) makes use of this feature if available, but Xen (validly)
fails the attempt to write the respective MSR. Hence the feature must be
hidden from PV guests.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: 2007-01-16/xen/arch/x86/traps.c
===================================================================
--- 2007-01-16.orig/xen/arch/x86/traps.c        2007-01-15 09:10:11.000000000 
+0100
+++ 2007-01-16/xen/arch/x86/traps.c     2007-02-01 17:25:28.000000000 +0100
@@ -597,6 +597,11 @@ static int emulate_forced_invalid_op(str
         if ( !IS_PRIV(current->domain) )
             clear_bit(X86_FEATURE_MTRR, &d);
     }
+    else if ( regs->eax == 0x80000001 )
+    {
+        /* Modify Feature Information. */
+        clear_bit(X86_FEATURE_RDTSCP % 32, &d);
+    }
     else
     {
         (void)cpuid_hypervisor_leaves(regs->eax, &a, &b, &c, &d);
Index: 2007-01-16/xen/include/asm-x86/cpufeature.h
===================================================================
--- 2007-01-16.orig/xen/include/asm-x86/cpufeature.h    2006-04-24 
15:28:58.000000000 +0200
+++ 2007-01-16/xen/include/asm-x86/cpufeature.h 2007-02-01 17:25:15.000000000 
+0100
@@ -49,6 +49,7 @@
 #define X86_FEATURE_MP         (1*32+19) /* MP Capable. */
 #define X86_FEATURE_NX         (1*32+20) /* Execute Disable */
 #define X86_FEATURE_MMXEXT     (1*32+22) /* AMD MMX extensions */
+#define X86_FEATURE_RDTSCP     (1*32+27) /* RDTSCP */
 #define X86_FEATURE_LM         (1*32+29) /* Long Mode (x86-64) */
 #define X86_FEATURE_3DNOWEXT   (1*32+30) /* AMD 3DNow! extensions */
 #define X86_FEATURE_3DNOW      (1*32+31) /* 3DNow! */


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