[PATCH 2/2] x86/svm: Intercept Bus Locks for HVM guests

[Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>]

With the threshold initialised to 1 the guest exits at the first
buslock. Initialising as zero is invalid and causes an immediate exit.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c  | 4 ++++
 xen/arch/x86/hvm/svm/vmcb.c | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 9748df87d8..dbb7f99d5e 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -3087,6 +3087,10 @@ void asmlinkage svm_vmexit_handler(void)
         hvm_descriptor_access_intercept(0, 0, desc, write);
         break;
     }
+    case VMEXIT_BUSLOCK:
+        perfc_incr(buslock);
+        vmcb->bus_lock_thresh = 1;
+        break;
 
     default:
     unexpected_exit_type:
diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
index cbee10d046..7a19b1ab61 100644
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -66,6 +66,12 @@ static int construct_vmcb(struct vcpu *v)
         GENERAL2_INTERCEPT_XSETBV      | GENERAL2_INTERCEPT_ICEBP       |
         GENERAL2_INTERCEPT_RDPRU;
 
+    if ( cpu_has_bus_lock_thresh )
+    {
+        vmcb->_general3_intercepts = GENERAL3_INTERCEPT_BUS_LOCK_THRESH;
+        vmcb->bus_lock_thresh = 1; /* trigger immediately */
+    }
+
     /* Intercept all debug-register writes. */
     vmcb->_dr_intercepts = ~0u;
 
-- 
2.43.0