[Xen-devel] [PATCH] x86: propagate disabled APIC state to Dom0

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

This in particular eliminates the need to specify "noapic" to Dom0 when
"noapic" is passed to Xen, provided the kernel side gets slightly
modified to make use of this information (Linux side patch cannot
easily be provided for the 2.6.18 tree, but this is being used by our
2.6.27-based one).

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

--- 2009-01-08.orig/xen/arch/x86/traps.c        2009-01-08 10:56:55.000000000 
+0100
+++ 2009-01-08/xen/arch/x86/traps.c     2009-01-09 09:42:42.000000000 +0100
@@ -723,6 +723,8 @@ static void pv_cpuid(struct cpu_user_reg
     {
         /* Modify Feature Information. */
         __clear_bit(X86_FEATURE_VME, &d);
+        if ( !cpu_has_apic )
+            __clear_bit(X86_FEATURE_APIC, &d);
         if ( !opt_allow_hugepage )
             __clear_bit(X86_FEATURE_PSE, &d);
         __clear_bit(X86_FEATURE_PGE, &d);
@@ -755,6 +757,8 @@ static void pv_cpuid(struct cpu_user_reg
         __clear_bit(X86_FEATURE_XTPR % 32, &c);
         __clear_bit(X86_FEATURE_PDCM % 32, &c);
         __clear_bit(X86_FEATURE_DCA % 32, &c);
+        if ( !cpu_has_apic )
+           __clear_bit(X86_FEATURE_X2APIC % 32, &c);
         __set_bit(X86_FEATURE_HYPERVISOR % 32, &c);
         break;
     case 0x80000001:
@@ -773,6 +777,8 @@ static void pv_cpuid(struct cpu_user_reg
         __clear_bit(X86_FEATURE_RDTSCP % 32, &d);
 
         __clear_bit(X86_FEATURE_SVME % 32, &c);
+        if ( !cpu_has_apic )
+           __clear_bit(X86_FEATURE_EXTAPICSPACE % 32, &c);
         __clear_bit(X86_FEATURE_OSVW % 32, &c);
         __clear_bit(X86_FEATURE_IBS % 32, &c);
         __clear_bit(X86_FEATURE_SKINIT % 32, &c);




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