[PATCH] x86/hvm: save/restore per-VCPU event channel upcall vector

[David Vrabel <dvrabel@xxxxxxxxxx>]

The Windows XENBUS driver sets the per-VCPU LAPIC vector for event
channel interrupts using the HVMOP_set_evtchn_upcall_vector hypercall
(rather than using a vector-type callback in the CALLBACK_IRQ HVM
parameter since the vectors might be different for different VCPUs).

This state needs to be saved/restored or a restored guest may not be
able to get an event channel interrupts.

Note that the Windows XENBUS driver workarounds this by reissuing the
hypercall when resuming after a migration, but this workaround would
not be possible in an guest transparent live migration or a live
update.

Signed-off-by: David Vrabel <dvrabel@xxxxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c                 | 50 ++++++++++++++++++++++++--
 xen/include/public/arch-x86/hvm/save.h | 12 ++++++-
 2 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 350dc396e3..be2e676c4a 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4071,6 +4071,52 @@ static int hvmop_flush_tlb_all(void)
     return paging_flush_tlb(NULL) ? 0 : -ERESTART;
 }
 
+static void hvm_set_evtchn_upcall_vector(struct vcpu *v, uint8_t vector)
+{
+    printk(XENLOG_G_INFO "%pv: upcall vector %02x\n", v, vector);
+
+    v->arch.hvm.evtchn_upcall_vector = vector;
+    hvm_assert_evtchn_irq(v);
+}
+
+static int hvm_save_evtchn_upcall_vector(
+    struct vcpu *v, hvm_domain_context_t *h)
+{
+    struct hvm_evtchn_upcall_vector upcall;
+
+    /* Skip record if VCPU is down or the upcall vector is not used. */
+    if ( test_bit(_VPF_down, &v->pause_flags) )
+        return 0;
+    if ( v->arch.hvm.evtchn_upcall_vector == 0 )
+        return 0;
+
+    upcall.vector = v->arch.hvm.evtchn_upcall_vector;
+
+    return hvm_save_entry(EVTCHN_UPCALL_VECTOR, v->vcpu_id, h, &upcall);
+}
+
+static int hvm_load_evtchn_upcall_vector(
+    struct domain *d, hvm_domain_context_t *h)
+{
+    unsigned int vcpuid;
+    struct vcpu *v;
+    struct hvm_evtchn_upcall_vector upcall;
+
+    vcpuid = hvm_load_instance(h);
+    if ( (v = domain_vcpu(d, vcpuid)) == NULL )
+        return -EINVAL;
+
+    if ( hvm_load_entry(EVTCHN_UPCALL_VECTOR, h, &upcall) != 0 )
+        return -EINVAL;
+
+    hvm_set_evtchn_upcall_vector(v, upcall.vector);
+
+    return 0;
+}
+
+HVM_REGISTER_SAVE_RESTORE(EVTCHN_UPCALL_VECTOR, hvm_save_evtchn_upcall_vector,
+                          hvm_load_evtchn_upcall_vector, 1, HVMSR_PER_VCPU);
+
 static int hvmop_set_evtchn_upcall_vector(
     XEN_GUEST_HANDLE_PARAM(xen_hvm_evtchn_upcall_vector_t) uop)
 {
@@ -4090,10 +4136,8 @@ static int hvmop_set_evtchn_upcall_vector(
     if ( (v = domain_vcpu(d, op.vcpu)) == NULL )
         return -ENOENT;
 
-    printk(XENLOG_G_INFO "%pv: upcall vector %02x\n", v, op.vector);
+    hvm_set_evtchn_upcall_vector(v, op.vector);
 
-    v->arch.hvm.evtchn_upcall_vector = op.vector;
-    hvm_assert_evtchn_irq(v);
     return 0;
 }
 
diff --git a/xen/include/public/arch-x86/hvm/save.h 
b/xen/include/public/arch-x86/hvm/save.h
index 773a380bc2..177cb09150 100644
--- a/xen/include/public/arch-x86/hvm/save.h
+++ b/xen/include/public/arch-x86/hvm/save.h
@@ -641,12 +641,22 @@ struct hvm_msr {
 
 #define CPU_MSR_CODE  20
 
+/**
+ * Per-VCPU event channel upcall vector as set by
+ * HVMOP_set_evtchn_upcall_vector hypercall.
+ */
+struct hvm_evtchn_upcall_vector {
+    uint8_t vector;
+};
+
+DECLARE_HVM_SAVE_TYPE(EVTCHN_UPCALL_VECTOR, 21, struct 
hvm_evtchn_upcall_vector);
+
 /* Range 22 - 34 (inclusive) reserved for Amazon */
 
 /*
  * Largest type-code in use
  */
-#define HVM_SAVE_CODE_MAX 20
+#define HVM_SAVE_CODE_MAX 21
 
 #endif /* __XEN_PUBLIC_HVM_SAVE_X86_H__ */
 
-- 
2.30.2