vm_event: support for guest-requested events

Added support for a new class of vm_events: VM_EVENT_REASON_REQUEST,
sent via HVMOP_request_vm_event. The guest can request that a
generic vm_event (containing only the vm_event-filled guest registers
as information) be sent to userspace by setting up the correct
registers and doing a VMCALL. For example, for a 32-bit guest, this
means: EAX = 34 (hvmop), EBX = 24 (HVMOP_guest_request_vm_event),
ECX = 0 (NULL required for the hypercall parameter, reserved).

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Tamas K Lengyel <tlengyel@novetta.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

tools/libxc/include/xenctrl.h

@@ -2378,6 +2378,8 @@ int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, bool enable,
 int xc_monitor_singlestep(xc_interface *xch, domid_t domain_id, bool enable);
 int xc_monitor_software_breakpoint(xc_interface *xch, domid_t domain_id,
                                    bool enable);
+int xc_monitor_guest_request(xc_interface *xch, domid_t domain_id,
+                             bool enable, bool sync);
 
 /***
  * Memory sharing operations.

tools/libxc/xc_monitor.c

@@ -129,3 +129,18 @@ int xc_monitor_singlestep(xc_interface *xch, domid_t domain_id,
 
     return do_domctl(xch, &domctl);
 }
+
+int xc_monitor_guest_request(xc_interface *xch, domid_t domain_id, bool enable,
+                             bool sync)
+{
+    DECLARE_DOMCTL;
+
+    domctl.cmd = XEN_DOMCTL_monitor_op;
+    domctl.domain = domain_id;
+    domctl.u.monitor_op.op = enable ? XEN_DOMCTL_MONITOR_OP_ENABLE
+                                    : XEN_DOMCTL_MONITOR_OP_DISABLE;
+    domctl.u.monitor_op.event = XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST;
+    domctl.u.monitor_op.u.guest_request.sync = sync;
+
+    return do_domctl(xch, &domctl);
+}

xen/arch/x86/hvm/event.c

@@ -126,6 +126,22 @@ void hvm_event_msr(unsigned int msr, uint64_t value)
         hvm_event_traps(1, &req);
 }
 
+void hvm_event_guest_request(void)
+{
+    struct vcpu *curr = current;
+    struct arch_domain *currad = &curr->domain->arch;
+
+    if ( currad->monitor.guest_request_enabled )
+    {
+        vm_event_request_t req = {
+            .reason = VM_EVENT_REASON_GUEST_REQUEST,
+            .vcpu_id = curr->vcpu_id,
+        };
+
+        hvm_event_traps(currad->monitor.guest_request_sync, &req);
+    }
+}
+
 int hvm_event_int3(unsigned long gla)
 {
     int rc = 0;

xen/arch/x86/hvm/hvm.c

@@ -5999,7 +5999,6 @@ static int hvmop_get_param(
 #define HVMOP_op_mask 0xff
 
 long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
-
 {
     unsigned long start_iter, mask;
     long rc = 0;
@@ -6413,6 +6412,13 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case HVMOP_guest_request_vm_event:
+        if ( guest_handle_is_null(arg) )
+            hvm_event_guest_request();
+        else
+            rc = -EINVAL;
+        break;
+
     default:
     {
         gdprintk(XENLOG_DEBUG, "Bad HVM op %ld.\n", op);

xen/arch/x86/monitor.c

@@ -55,7 +55,8 @@ static inline uint32_t get_capabilities(struct domain *d)
 
     capabilities = (1 << XEN_DOMCTL_MONITOR_EVENT_WRITE_CTRLREG) |
                    (1 << XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR) |
-                   (1 << XEN_DOMCTL_MONITOR_EVENT_SOFTWARE_BREAKPOINT);
+                   (1 << XEN_DOMCTL_MONITOR_EVENT_SOFTWARE_BREAKPOINT) |
+                   (1 << XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST);
 
     /* Since we know this is on VMX, we can just call the hvm func */
     if ( hvm_is_singlestep_supported() )
@@ -184,6 +185,22 @@ int monitor_domctl(struct domain *d, struct xen_domctl_monitor_op *mop)
         break;
     }
 
+    case XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST:
+    {
+        bool_t status = ad->monitor.guest_request_enabled;
+
+        rc = status_check(mop, status);
+        if ( rc )
+            return rc;
+
+        ad->monitor.guest_request_sync = mop->u.guest_request.sync;
+
+        domain_pause(d);
+        ad->monitor.guest_request_enabled = !status;
+        domain_unpause(d);
+        break;
+    }
+
     default:
         return -EOPNOTSUPP;
 

xen/include/asm-x86/domain.h

@@ -347,13 +347,15 @@ struct arch_domain
 
     /* Monitor options */
     struct {
-        uint16_t write_ctrlreg_enabled       : 4;
-        uint16_t write_ctrlreg_sync          : 4;
-        uint16_t write_ctrlreg_onchangeonly  : 4;
-        uint16_t mov_to_msr_enabled          : 1;
-        uint16_t mov_to_msr_extended         : 1;
-        uint16_t singlestep_enabled          : 1;
-        uint16_t software_breakpoint_enabled : 1;
+        unsigned int write_ctrlreg_enabled       : 4;
+        unsigned int write_ctrlreg_sync          : 4;
+        unsigned int write_ctrlreg_onchangeonly  : 4;
+        unsigned int mov_to_msr_enabled          : 1;
+        unsigned int mov_to_msr_extended         : 1;
+        unsigned int singlestep_enabled          : 1;
+        unsigned int software_breakpoint_enabled : 1;
+        unsigned int guest_request_enabled       : 1;
+        unsigned int guest_request_sync          : 1;
     } monitor;
 
     /* Mem_access emulation control */

xen/include/asm-x86/hvm/event.h

@@ -26,6 +26,7 @@ void hvm_event_msr(unsigned int msr, uint64_t value);
 /* Called for current VCPU: returns -1 if no listener */
 int hvm_event_int3(unsigned long gla);
 int hvm_event_single_step(unsigned long gla);
+void hvm_event_guest_request(void);
 
 #endif /* __ASM_X86_HVM_EVENT_H__ */
 

xen/include/public/domctl.h

@@ -1009,6 +1009,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_psr_cmt_op_t);
 #define XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR            1
 #define XEN_DOMCTL_MONITOR_EVENT_SINGLESTEP            2
 #define XEN_DOMCTL_MONITOR_EVENT_SOFTWARE_BREAKPOINT   3
+#define XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST         4
 
 struct xen_domctl_monitor_op {
     uint32_t op; /* XEN_DOMCTL_MONITOR_OP_* */
@@ -1039,6 +1040,11 @@ struct xen_domctl_monitor_op {
             /* Enable the capture of an extended set of MSRs */
             uint8_t extended_capture;
         } mov_to_msr;
+
+        struct {
+            /* Pause vCPU until response */
+            uint8_t sync;
+        } guest_request;
     } u;
 };
 typedef struct xen_domctl_monitor_op xen_domctl_monitor_op_t;

xen/include/public/hvm/hvm_op.h

@@ -396,6 +396,8 @@ DEFINE_XEN_GUEST_HANDLE(xen_hvm_evtchn_upcall_vector_t);
 
 #endif /* defined(__i386__) || defined(__x86_64__) */
 
+#define HVMOP_guest_request_vm_event 24
+
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
 
 /*

xen/include/public/vm_event.h

@@ -95,6 +95,8 @@
 #define VM_EVENT_REASON_SOFTWARE_BREAKPOINT     6
 /* Single-step (e.g. MTF) */
 #define VM_EVENT_REASON_SINGLESTEP              7
+/* An event has been requested via HVMOP_guest_request_vm_event. */
+#define VM_EVENT_REASON_GUEST_REQUEST           8
 
 /* Supported values for the vm_event_write_ctrlreg index. */
 #define VM_EVENT_X86_CR0    0