[Xen-devel] [PATCH]x86:x2apic: Disable x2apic on x86-32 permanently

["Zhang, Fengzhe" <fengzhe.zhang@xxxxxxxxx>]

x86:x2apic: Disable x2apic on x86-32 permanently

x2apic initialization on x86_32 uses vcpu pointer before it is initialized. As 
x2apic is unlikely to be used on x86_32, this patch disables x2apic permanently 
on x86_32. It also asserts the sanity of vcpu pointer before dereference to 
prevent further misuse.

Signed-off-by: Fengzhe Zhang <fengzhe.zhang@xxxxxxxxx>

diff -r 02c0af2bf280 xen/arch/x86/apic.c
--- a/xen/arch/x86/apic.c       Mon Jan 17 18:05:52 2011 +0000
+++ b/xen/arch/x86/apic.c       Wed Jan 19 03:24:16 2011 -0500
@@ -961,6 +961,22 @@
     if ( !cpu_has_x2apic )
         return;

+#ifdef __i386__
+    clear_bit(X86_FEATURE_X2APIC, boot_cpu_data.x86_capability);
+    if (x2apic_enabled) {
+        uint64_t msr_content;
+
+        rdmsrl(MSR_IA32_APICBASE, msr_content);
+        msr_content &= ~(MSR_IA32_APICBASE_ENABLE | MSR_IA32_APICBASE_EXTD);
+        wrmsrl(MSR_IA32_APICBASE, msr_content);
+        msr_content |= MSR_IA32_APICBASE_ENABLE;
+        wrmsrl(MSR_IA32_APICBASE, msr_content);
+        x2apic_enabled = 0;
+    }
+    printk("x2APIC disabled permanently on x86_32.\n");
+    return;
+#endif
+
     if ( !opt_x2apic )
     {
         if ( !x2apic_enabled )
diff -r 02c0af2bf280 xen/arch/x86/x86_32/domain_page.c
--- a/xen/arch/x86/x86_32/domain_page.c Mon Jan 17 18:05:52 2011 +0000
+++ b/xen/arch/x86/x86_32/domain_page.c Wed Jan 19 03:24:16 2011 -0500
@@ -53,6 +53,8 @@
     perfc_incr(map_domain_page_count);

     v = mapcache_current_vcpu();
+    /* Prevent vcpu pointer being used before initialize. */
+    ASSERT((unsigned long)v != 0xfffff000);

     dcache = &v->domain->arch.mapcache;
     vcache = &v->arch.mapcache;

Attachment: x2apic_fix.patch
Description: x2apic_fix.patch

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