[PATCH v2 2/3] x86/svm: Intercept Bus Locks for HVM guests

[Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>]

Configure the Bus Lock intercept when supported by the host. The
VMCB counter is initialised to zero so it fires upon the first
instruction that locks the bus. On the #VMEXIT handler that counter
is set to 1 because it has fault behaviour and the offending instruction
needs to re-execute.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
v2:
 * Moved the P() call to this patch. We don't want to print until
   the feature is fully supported.
 * Removed the initialisation of the counter to 1 in vmcb.c, so it's
   implicitly zero-initialised.
---
 xen/arch/x86/hvm/svm/svm.c  | 6 ++++++
 xen/arch/x86/hvm/svm/vmcb.c | 3 +++
 xen/arch/x86/hvm/svm/vmcb.h | 4 ++--
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 5d23603fc1..abda5a9063 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2524,6 +2524,7 @@ const struct hvm_function_table * __init start_svm(void)
     P(cpu_has_tsc_ratio, "TSC Rate MSR");
     P(cpu_has_svm_sss, "NPT Supervisor Shadow Stack");
     P(cpu_has_svm_spec_ctrl, "MSR_SPEC_CTRL virtualisation");
+    P(cpu_has_svm_bus_lock, "BusLock-Intercept Filter");
 #undef P
 
     if ( !printed )
@@ -3087,6 +3088,11 @@ void asmlinkage svm_vmexit_handler(void)
         break;
     }
 
+    case VMEXIT_BUS_LOCK:
+        perfc_incr(buslock);
+        vmcb->bus_lock_count = 1;
+        break;
+
     default:
     unexpected_exit_type:
         gprintk(XENLOG_ERR, "Unexpected vmexit: reason %#"PRIx64", "
diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
index cbee10d046..15223a693e 100644
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -66,6 +66,9 @@ static int construct_vmcb(struct vcpu *v)
         GENERAL2_INTERCEPT_XSETBV      | GENERAL2_INTERCEPT_ICEBP       |
         GENERAL2_INTERCEPT_RDPRU;
 
+    if ( cpu_has_svm_bus_lock )
+        vmcb->_general3_intercepts |= GENERAL3_INTERCEPT_BUS_LOCK;
+
     /* Intercept all debug-register writes. */
     vmcb->_dr_intercepts = ~0u;
 
diff --git a/xen/arch/x86/hvm/svm/vmcb.h b/xen/arch/x86/hvm/svm/vmcb.h
index 231f9b1b06..68cf5eaf0b 100644
--- a/xen/arch/x86/hvm/svm/vmcb.h
+++ b/xen/arch/x86/hvm/svm/vmcb.h
@@ -68,7 +68,7 @@ enum GenericIntercept2bits
 /* general 3 intercepts */
 enum GenericIntercept3bits
 {
-    GENERAL3_INTERCEPT_BUS_LOCK_THRESH = 1 << 5,
+    GENERAL3_INTERCEPT_BUS_LOCK = 1 << 5,
 };
 
 /* control register intercepts */
@@ -497,7 +497,7 @@ struct vmcb_struct {
     u8  guest_ins_len;          /* offset 0xD0 */
     u8  guest_ins[15];          /* offset 0xD1 */
     u64 res10a[8];              /* offset 0xE0 */
-    u16 bus_lock_thresh;        /* offset 0x120 */
+    u16 bus_lock_count;         /* offset 0x120 */
     u16 res10b[3];              /* offset 0x122 */
     u64 res10c[91];             /* offset 0x128 pad to save area */
 
-- 
2.43.0