xen/vcpu: Handle xen_vcpu_setup() failure in hotplug

The hypercall VCPUOP_register_vcpu_info can fail. This failure is
handled by making per_cpu(xen_vcpu, cpu) point to its shared_info
slot and those without one (cpu >= MAX_VIRT_CPUS) be NULL.

For PVH/PVHVM, this is not enough, because we also need to pull
these VCPUs out of circulation.

Fix for PVH/PVHVM: on registration failure in the cpuhp prepare
callback (xen_cpu_up_prepare_hvm()), return an error to the cpuhp
state-machine so it can fail the CPU init.

Fix for PV: the registration happens before smp_init(), so, in the
failure case we clamp setup_max_cpus and limit the number of VCPUs
that smp_init() will bring-up to MAX_VIRT_CPUS.
This is functionally correct but it makes the code a bit simpler
if we get rid of this explicit clamping: for VCPUs that don't have
valid xen_vcpu, fail the CPU init in the cpuhp prepare callback
(xen_cpu_up_prepare_pv()).

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 90828256248b..0d5004477db6 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -78,7 +78,7 @@ bool xen_vcpu_stolen(int vcpu);
 
 extern int xen_have_vcpu_info_placement;
 
-void xen_vcpu_setup(int cpu);
+int xen_vcpu_setup(int cpu);
 void xen_vcpu_info_reset(int cpu);
 void xen_setup_vcpu_info_placement(void);