[Xen-devel] [PATCH v2] x86/hvm: Allow guest_request vm_events coming from userspace

[Alexandru Isaila <aisaila@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").
This is a use case in communication between a userspace application
in the guest and the introspection application in dom0.

Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>

---
Changes since V1:
        - Added Fallthrough check on mode == 2
---
 xen/arch/x86/hvm/hypercall.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
index e7238ce..1c067c3 100644
--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -152,9 +152,15 @@ int hvm_hypercall(struct cpu_user_regs *regs)
     {
     case 8:
         eax = regs->rax;
+        if ( eax == __HYPERVISOR_hvm_op &&
+             regs->rdi == HVMOP_guest_request_vm_event )
+            break;
         /* Fallthrough to permission check. */
     case 4:
     case 2:
+        if ( mode != 8 && eax == __HYPERVISOR_hvm_op &&
+             regs->ebx == HVMOP_guest_request_vm_event )
+            break;
         if ( unlikely(hvm_get_cpl(curr)) )
         {
     default:
-- 
2.7.4


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