x86/xen: mark boot CPU of PV guest in MSR_IA32_APICBASE

Recent topology checks of the x86 boot code uncovered the need for
PV guests to have the boot cpu marked in the APICBASE MSR.

Fixes: 9d22c963 ("x86/topology: Handle bogus ACPI tables correctly")
Reported-by: Niels Dettenbach <nd@syndicat.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/enlighten_pv.c

@@ -1032,6 +1032,10 @@ static u64 xen_do_read_msr(unsigned int msr, int *err)
 	switch (msr) {
 	case MSR_IA32_APICBASE:
 		val &= ~X2APIC_ENABLE;
+		if (smp_processor_id() == 0)
+			val |= MSR_IA32_APICBASE_BSP;
+		else
+			val &= ~MSR_IA32_APICBASE_BSP;
 		break;
 	}
 	return val;