x86/kexec: fix kexec on systems which boot in x2apic mode

Moving straight from fully disabled to x2apic mode is an illegal state
transition, and causes an unconditional #GP fault.  Bounce through xapic mode
to avoid the fault.

In addition, avoid bouncing through the various apic modes if the mode is
already correct.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index 0e5e302ec1c744cc52b174ffea9401880a6454d5..bbcc0a16d04c6e5fed30c9459d7f194ff8af8aaf 100644 (file)
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -314,7 +314,7 @@ void disable_local_APIC(void)
                ~(MSR_IA32_APICBASE_ENABLE|MSR_IA32_APICBASE_EXTD));
     }
 
-    if ( kexecing )
+    if ( kexecing && (current_local_apic_mode() != apic_boot_mode) )
     {
         uint64_t msr_content;
         rdmsrl(MSR_IA32_APICBASE, msr_content);
@@ -330,7 +330,9 @@ void disable_local_APIC(void)
             wrmsrl(MSR_IA32_APICBASE, msr_content);
             break;
         case APIC_MODE_X2APIC:
-            msr_content |= (MSR_IA32_APICBASE_ENABLE|MSR_IA32_APICBASE_EXTD);
+            msr_content |= MSR_IA32_APICBASE_ENABLE;
+            wrmsrl(MSR_IA32_APICBASE, msr_content);
+            msr_content |= MSR_IA32_APICBASE_EXTD;
             wrmsrl(MSR_IA32_APICBASE, msr_content);
             break;
         default: