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xen/pvh*: Support > 32 VCPUs at domain restore

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When Xen restores a PVHVM or PVH guest, its shared_info only holds
up to 32 CPUs. The hypercall VCPUOP_register_vcpu_info allows
us to setup per-page areas for VCPUs. This means we can boot
PVH* guests with more than 32 VCPUs. During restore the per-cpu
structure is allocated freshly by the hypervisor (vcpu_info_mfn is
set to INVALID_MFN) so that the newly restored guest can make a
VCPUOP_register_vcpu_info hypercall.

However, we end up triggering this condition in Xen:
/* Run this command on yourself or on other offline VCPUS. */
 if ( (v != current) && !test_bit(_VPF_down, &v->pause_flags) )

which means we are unable to setup the per-cpu VCPU structures
for running VCPUS. The Linux PV code paths makes this work by
iterating over cpu_possible in xen_vcpu_restore() with:

 1) is target CPU up (VCPUOP_is_up hypercall?)
 2) if yes, then VCPUOP_down to pause it
 3) VCPUOP_register_vcpu_info
 4) if it was down, then VCPUOP_up to bring it back up

With Xen commit 192df6f9122d ("xen/x86: allow HVM guests to use
hypercalls to bring up vCPUs") this is available for non-PV guests.
As such first check if VCPUOP_is_up is actually possible before
trying this dance.

As most of this dance code is done already in xen_vcpu_restore()
let's make it callable on PV, PVH and PVHVM.

Based-on-patch-by: Konrad Wilk <konrad.wilk@oracle.com>
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 17:05:59 -07:00
committed by Juergen Gross
parent ad73fd595c
commit 0b64ffb8db
5 changed files with 54 additions and 34 deletions
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10
arch/x86/xen/smp_hvm.c
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@@ -28,10 +28,20 @@ static void __init xen_hvm_smp_prepare_boot_cpu(void)
static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
{
int cpu;
native_smp_prepare_cpus(max_cpus);
WARN_ON(xen_smp_intr_init(0));
xen_init_lock_cpu(0);
for_each_possible_cpu(cpu) {
if (cpu == 0)
continue;
/* Set default vcpu_id to make sure that we don't use cpu-0's */
per_cpu(xen_vcpu_id, cpu) = XEN_VCPU_ID_INVALID;
}
}
#ifdef CONFIG_HOTPLUG_CPU