xen: introduce xen_vcpu_id mapping

It may happen that Xen's and Linux's ideas of vCPU id diverge. In
particular, when we crash on a secondary vCPU we may want to do kdump
and unlike plain kexec where we do migrate_to_reboot_cpu() we try
booting on the vCPU which crashed. This doesn't work very well for
PVHVM guests as we have a number of hypercalls where we pass vCPU id
as a parameter. These hypercalls either fail or do something
unexpected.

To solve the issue introduce percpu xen_vcpu_id mapping. ARM and PV
guests get direct mapping for now. Boot CPU for PVHVM guest gets its
id from CPUID. With secondary CPUs it is a bit more
trickier. Currently, we initialize IPI vectors before these CPUs boot
so we can't use CPUID. Use ACPI ids from MADT instead.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 355275bad2cf..c9c532d56623 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -9,6 +9,12 @@
 
 DECLARE_PER_CPU(struct vcpu_info *, xen_vcpu);
 
+DECLARE_PER_CPU(int, xen_vcpu_id);
+static inline int xen_vcpu_nr(int cpu)
+{
+        return per_cpu(xen_vcpu_id, cpu);
+}
+
 void xen_arch_pre_suspend(void);
 void xen_arch_post_suspend(int suspend_cancelled);