x86/paravirt: add debugging for missing operations

Rather than just jumping to 0 when there's a missing operation, raise a BUG.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 15 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9441e46cb49b..67e5275f03c8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -435,6 +435,13 @@ config PARAVIRT_CLOCK
 
 endif
 
+config PARAVIRT_DEBUG
+       bool "paravirt-ops debugging"
+       depends on PARAVIRT && DEBUG_KERNEL
+       help
+         Enable to debug paravirt_ops internals.  Specifically, BUG if
+         a paravirt_op is missing when it is called.
+
 config MEMTEST
         bool "Memtest"
         depends on X86_64
diff --git a/include/asm-x86/paravirt.h b/include/asm-x86/paravirt.h
index 5467e2cff4bc..198293bed46f 100644
--- a/include/asm-x86/paravirt.h
+++ b/include/asm-x86/paravirt.h
@@ -459,10 +459,17 @@ int paravirt_disable_iospace(void);
 #define VEXTRA_CLOBBERS  , "rax", "r8", "r9", "r10", "r11"
 #endif
 
+#ifdef CONFIG_PARAVIRT_DEBUG
+#define PVOP_TEST_NULL(op)      BUG_ON(op == NULL)
+#else
+#define PVOP_TEST_NULL(op)      ((void)op)
+#endif
+
 #define __PVOP_CALL(rettype, op, pre, post, ...)                        \
         ({                                                              \
                 rettype __ret;                                          \
                 PVOP_CALL_ARGS;                                 \
+                PVOP_TEST_NULL(op);                                     \
                 /* This is 32-bit specific, but is okay in 64-bit */    \
                 /* since this condition will never hold */              \
                 if (sizeof(rettype) > sizeof(unsigned long)) {          \
@@ -491,6 +498,7 @@ int paravirt_disable_iospace(void);
 #define __PVOP_VCALL(op, pre, post, ...)                                \
         ({                                                              \
                 PVOP_VCALL_ARGS;                                        \
+                PVOP_TEST_NULL(op);                                     \
                 asm volatile(pre                                        \
                              paravirt_alt(PARAVIRT_CALL)                \
                              post                                       \