[Xen-devel] [PATCH V2] x86/hvm: Allow guest_request vm_events coming from userspace

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

Allow guest userspace code to request that a vm_event be sent out
via VMCALL. This functionality seems to be handy for a number of
Xen developers, as stated on the mailing list (thread "[Xen-devel]
HVMOP_guest_request_vm_event only works from guest in ring0").

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

---
Changes since V1:
 - No longer repeating the check when mode == 8.
 - Added /* Fallthrough */ tags for Coverity.
---
 xen/arch/x86/hvm/hvm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 893eff6..cb546e4 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4146,15 +4146,25 @@ int hvm_do_hypercall(struct cpu_user_regs *regs)
     switch ( mode )
     {
     case 8:        
+        if ( eax == __HYPERVISOR_hvm_op &&
+             regs->rdi == HVMOP_guest_request_vm_event )
+            break;
+        /* Fallthrough */
     case 4:
+        /* Fallthrough */
     case 2:
+        if ( mode != 8 && eax == __HYPERVISOR_hvm_op &&
+             regs->_ebx == HVMOP_guest_request_vm_event )
+            break;
         hvm_get_segment_register(curr, x86_seg_ss, &sreg);
         if ( unlikely(sreg.attr.fields.dpl) )
         {
+        /* Fallthrough */
     default:
             regs->eax = -EPERM;
             return HVM_HCALL_completed;
         }
+        /* Fallthrough */
     case 0:
         break;
     }
-- 
1.9.1


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