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xen/vcpu: Handle xen_vcpu_setup() failure in hotplug

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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>
This commit is contained in:
Ankur Arora
2017-06-02 17:06:01 -07:00
committed by Juergen Gross
parent 0e4d583723
commit c9b5d98b25
4 changed files with 45 additions and 26 deletions
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14
arch/x86/xen/enlighten_pv.c
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@@ -958,7 +958,16 @@ void __ref xen_setup_vcpu_info_placement(void)
for_each_possible_cpu(cpu) {
/* Set up direct vCPU id mapping for PV guests. */
per_cpu(xen_vcpu_id, cpu) = cpu;
xen_vcpu_setup(cpu);
/*
* xen_vcpu_setup(cpu) can fail -- in which case it
* falls back to the shared_info version for cpus
* where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.
*
* xen_cpu_up_prepare_pv() handles the rest by failing
* them in hotplug.
*/
(void) xen_vcpu_setup(cpu);
}
/*
@@ -1432,6 +1441,9 @@ static int xen_cpu_up_prepare_pv(unsigned int cpu)
{
int rc;
if (per_cpu(xen_vcpu, cpu) == NULL)
return -ENODEV;
xen_setup_timer(cpu);
rc = xen_smp_intr_init(cpu);