[PATCH RFC 1/1] Introduce VCPUOP_reset_vcpu_info

[Vitaly Kuznetsov <vkuznets@redhat.com>]

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

When an SMP guest performs kexec/kdump it tries issuing VCPUOP_register_vcpu_info.
This fails due to vcpu_info already being registered. Introduce new vcpu operation
to reset vcpu_info to its default state.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 xen/arch/x86/hvm/hvm.c    |  1 +
 xen/common/domain.c       | 22 +++++++++++++++++++---
 xen/include/public/vcpu.h |  6 ++++++
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 216c3f2..7917272 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3332,6 +3332,7 @@ static long hvm_vcpu_op(
     case VCPUOP_set_singleshot_timer:
     case VCPUOP_stop_singleshot_timer:
     case VCPUOP_register_vcpu_info:
+    case VCPUOP_reset_vcpu_info:
     case VCPUOP_register_vcpu_time_memory_area:
         rc = do_vcpu_op(cmd, vcpuid, arg);
         break;
diff --git a/xen/common/domain.c b/xen/common/domain.c
index ac444ba..024f366 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -961,9 +961,9 @@ int map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned offset)
 }
 
 /*
- * Unmap the vcpu info page if the guest decided to place it somewhere
- * else.  This is only used from arch_domain_destroy, so there's no
- * need to do anything clever.
+ * Unmap the vcpu info page if the guest decided to place it somewhere else.
+ * This is used from arch_domain_destroy and from VCPUOP_reset_vcpu_info
+ * handler.
  */
 void unmap_vcpu_info(struct vcpu *v)
 {
@@ -1121,6 +1121,22 @@ long do_vcpu_op(int cmd, int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case VCPUOP_reset_vcpu_info:
+    {
+        struct domain *d = v->domain;
+
+        if ( !test_bit(_VPF_down, &v->pause_flags) )
+            return -EFAULT;
+
+        domain_lock(d);
+        unmap_vcpu_info(v);
+        if ( vcpuid < XEN_LEGACY_MAX_VCPUS )
+            v->vcpu_info = (vcpu_info_t *)&shared_info(d, vcpu_info[vcpuid]);
+        domain_unlock(d);
+        rc = 0;
+        break;
+    }
+
     case VCPUOP_register_runstate_memory_area:
     {
         struct vcpu_register_runstate_memory_area area;
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index e888daf..c0283bc 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -227,6 +227,12 @@ struct vcpu_register_time_memory_area {
 typedef struct vcpu_register_time_memory_area vcpu_register_time_memory_area_t;
 DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
 
+/*
+ * Reset all of the vcpu_info information from their previous location
+ * to the default one used at bootup.
+ */
+#define VCPUOP_reset_vcpu_info   14
+
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
 /*
-- 
1.9.3