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| author | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2013-05-05 14:51:47 +0200 |
|---|---|---|
| committer | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2013-05-07 16:05:34 +0200 |
| commit | a520996ae2e2792e1f90b74e67c974120c8a3b83 (patch) | |
| tree | f853e587a26c19707e797e967a8003a24fe544a5 /arch | |
| parent | xen/vcpu/pvhvm: Fix vcpu hotplugging hanging. (diff) | |
| download | linux-a520996ae2e2792e1f90b74e67c974120c8a3b83.tar.xz linux-a520996ae2e2792e1f90b74e67c974120c8a3b83.zip | |
xen/vcpu: Document the xen_vcpu_info and xen_vcpu
They are important structures and it is not clear at first
look what they are for.
The xen_vcpu is a pointer. By default it points to the shared_info
structure (at the CPU offset location). However if the
VCPUOP_register_vcpu_info hypercall is implemented we can make the
xen_vcpu pointer point to a per-CPU location.
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
[v1: Added comments from Ian Campbell]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/xen/enlighten.c | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 94a81f41e8a2..a2babdb13a26 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -85,7 +85,29 @@ EXPORT_SYMBOL_GPL(hypercall_page); +/* + * Pointer to the xen_vcpu_info structure or + * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info + * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info + * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point + * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to + * acknowledge pending events. + * Also more subtly it is used by the patched version of irq enable/disable + * e.g. xen_irq_enable_direct and xen_iret in PV mode. + * + * The desire to be able to do those mask/unmask operations as a single + * instruction by using the per-cpu offset held in %gs is the real reason + * vcpu info is in a per-cpu pointer and the original reason for this + * hypercall. + * + */ DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu); + +/* + * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info + * hypercall. This can be used both in PV and PVHVM mode. The structure + * overrides the default per_cpu(xen_vcpu, cpu) value. + */ DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info); enum xen_domain_type xen_domain_type = XEN_NATIVE; @@ -187,7 +209,12 @@ static void xen_vcpu_setup(int cpu) /* Check to see if the hypervisor will put the vcpu_info structure where we want it, which allows direct access via - a percpu-variable. */ + a percpu-variable. + N.B. This hypercall can _only_ be called once per CPU. Subsequent + calls will error out with -EINVAL. This is due to the fact that + hypervisor has no unregister variant and this hypercall does not + allow to over-write info.mfn and info.offset. + */ err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info); if (err) { |