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

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>

5 files changed, 54 insertions, 34 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 96b745e3f56c..276cc21619ec 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -106,6 +106,21 @@ int xen_cpuhp_setup(int (*cpu_up_prepare_cb)(unsigned int),
         return rc >= 0 ? 0 : rc;
 }
 
+static void xen_vcpu_setup_restore(int cpu)
+{
+        /* Any per_cpu(xen_vcpu) is stale, so reset it */
+        xen_vcpu_info_reset(cpu);
+
+        /*
+         * For PVH and PVHVM, setup online VCPUs only. The rest will
+         * be handled by hotplug.
+         */
+        if (xen_pv_domain() ||
+            (xen_hvm_domain() && cpu_online(cpu))) {
+                xen_vcpu_setup(cpu);
+        }
+}
+
 /*
  * On restore, set the vcpu placement up again.
  * If it fails, then we're in a bad state, since
@@ -117,17 +132,23 @@ void xen_vcpu_restore(void)
 
         for_each_possible_cpu(cpu) {
                 bool other_cpu = (cpu != smp_processor_id());
-                bool is_up = HYPERVISOR_vcpu_op(VCPUOP_is_up, xen_vcpu_nr(cpu),
-                                                NULL);
+                bool is_up;
+
+                if (xen_vcpu_nr(cpu) == XEN_VCPU_ID_INVALID)
+                        continue;
+
+                /* Only Xen 4.5 and higher support this. */
+                is_up = HYPERVISOR_vcpu_op(VCPUOP_is_up,
+                                           xen_vcpu_nr(cpu), NULL) > 0;
 
                 if (other_cpu && is_up &&
                     HYPERVISOR_vcpu_op(VCPUOP_down, xen_vcpu_nr(cpu), NULL))
                         BUG();
 
-                xen_setup_runstate_info(cpu);
+                if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))
+                        xen_setup_runstate_info(cpu);
 
-                if (xen_have_vcpu_info_placement)
-                        xen_vcpu_setup(cpu);
+                xen_vcpu_setup_restore(cpu);
 
                 if (other_cpu && is_up &&
                     HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))
@@ -163,11 +184,11 @@ void xen_vcpu_setup(int cpu)
         BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
 
         /*
-         * This path is called twice on PVHVM - first during bootup via
-         * smp_init -> xen_hvm_cpu_notify, and then if the VCPU is being
-         * hotplugged: cpu_up -> xen_hvm_cpu_notify.
-         * As we can only do the VCPUOP_register_vcpu_info once lets
-         * not over-write its result.
+         * This path is called on PVHVM at bootup (xen_hvm_smp_prepare_boot_cpu)
+         * and at restore (xen_vcpu_restore). Also called for hotplugged
+         * VCPUs (cpu_init -> xen_hvm_cpu_prepare_hvm).
+         * However, the hypercall can only be done once (see below) so if a VCPU
+         * is offlined and comes back online then let's not redo the hypercall.
          *
          * For PV it is called during restore (xen_vcpu_restore) and bootup
          * (xen_setup_vcpu_info_placement). The hotplug mechanism does not
@@ -178,8 +199,6 @@ void xen_vcpu_setup(int cpu)
                         return;
         }
 
-        xen_vcpu_info_reset(cpu);
-
         if (xen_have_vcpu_info_placement) {
                 vcpup = &per_cpu(xen_vcpu_info, cpu);
                 info.mfn = arbitrary_virt_to_mfn(vcpup);
@@ -214,7 +233,7 @@ void xen_vcpu_setup(int cpu)
         if (!xen_have_vcpu_info_placement) {
                 if (cpu >= MAX_VIRT_CPUS)
                         clamp_max_cpus();
-                return;
+                xen_vcpu_info_reset(cpu);
         }
 }
 
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index eb53da6547ee..ba1afadb2512 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -20,7 +20,6 @@
 
 void __ref xen_hvm_init_shared_info(void)
 {
-        int cpu;
         struct xen_add_to_physmap xatp;
         static struct shared_info *shared_info_page;
 
@@ -35,18 +34,6 @@ void __ref xen_hvm_init_shared_info(void)
                 BUG();
 
         HYPERVISOR_shared_info = (struct shared_info *)shared_info_page;
-
-        /* xen_vcpu is a pointer to the vcpu_info struct in the shared_info
-         * page, we use it in the event channel upcall and in some pvclock
-         * related functions. We don't need the vcpu_info placement
-         * optimizations because we don't use any pv_mmu or pv_irq op on
-         * HVM.
-         * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
-         * online but xen_hvm_init_shared_info is run at resume time too and
-         * in that case multiple vcpus might be online. */
-        for_each_online_cpu(cpu) {
-                xen_vcpu_info_reset(cpu);
-        }
 }
 
 static void __init init_hvm_pv_info(void)
@@ -150,6 +137,13 @@ static void __init xen_hvm_guest_init(void)
 
         xen_hvm_init_shared_info();
 
+        /*
+         * xen_vcpu is a pointer to the vcpu_info struct in the shared_info
+         * page, we use it in the event channel upcall and in some pvclock
+         * related functions.
+         */
+        xen_vcpu_info_reset(0);
+
         xen_panic_handler_init();
 
         if (xen_feature(XENFEAT_hvm_callback_vector))
diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c
index 9e0fb9a015d4..6c8a805819ff 100644
--- a/arch/x86/xen/smp_hvm.c
+++ b/arch/x86/xen/smp_hvm.c
@@ -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
diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
index 01afcadde50a..484999416d8b 100644
--- a/arch/x86/xen/suspend_hvm.c
+++ b/arch/x86/xen/suspend_hvm.c
@@ -8,15 +8,10 @@
 
 void xen_hvm_post_suspend(int suspend_cancelled)
 {
-        int cpu;
-
-        if (!suspend_cancelled)
+        if (!suspend_cancelled) {
                 xen_hvm_init_shared_info();
+                xen_vcpu_restore();
+        }
         xen_callback_vector();
         xen_unplug_emulated_devices();
-        if (xen_feature(XENFEAT_hvm_safe_pvclock)) {
-                for_each_online_cpu(cpu) {
-                        xen_setup_runstate_info(cpu);
-                }
-        }
 }
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index c44a2ee8c8f8..218e6aae5433 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -15,6 +15,8 @@ static inline uint32_t xen_vcpu_nr(int cpu)
         return per_cpu(xen_vcpu_id, cpu);
 }
 
+#define XEN_VCPU_ID_INVALID U32_MAX
+
 void xen_arch_pre_suspend(void);
 void xen_arch_post_suspend(int suspend_cancelled);