[Xen-devel] [PATCH v2 2/4] VMX: move various uses of UD2 out of fast paths

["Jan Beulich" <JBeulich@xxxxxxxx>]

... at once making conditional forward jumps, which are statically
predicted to be not taken, only used for the unlikely (error) cases.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Fix #UD recovery for INVVPID (unintended flow change spotted by Andrew 
Cooper).

--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -67,6 +67,30 @@ void ret_from_intr(void);
 #define ASSERT_NOT_IN_ATOMIC
 #endif
 
+#else
+
+#ifdef __clang__ /* clang's builtin assember can't do .subsection */
+
+#define UNLIKELY_START_SECTION ".pushsection .fixup,\"ax\""
+#define UNLIKELY_END_SECTION   ".popsection"
+
+#else
+
+#define UNLIKELY_START_SECTION ".subsection 1"
+#define UNLIKELY_END_SECTION   ".subsection 0"
+
+#endif
+
+#define UNLIKELY_START(cond, tag)          \
+        "j" #cond " .Lunlikely%=.tag;\n\t" \
+        UNLIKELY_START_SECTION "\n"        \
+        ".Lunlikely%=.tag:"
+
+#define UNLIKELY_END(tag)                  \
+        "jmp .Llikely%=.tag;\n\t"          \
+        UNLIKELY_END_SECTION "\n"          \
+        ".Llikely%=.tag:"
+
 #endif
 
 #endif /* __X86_ASM_DEFNS_H__ */
--- a/xen/include/asm-x86/hvm/vmx/vmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h
@@ -285,7 +285,9 @@ static inline void __vmptrld(u64 addr)
     asm volatile ( VMPTRLD_OPCODE
                    MODRM_EAX_06
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 1f ; ud2 ; 1:\n"
+                   UNLIKELY_START(be, vmptrld)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION
                    :
                    : "a" (&addr)
                    : "memory");
@@ -296,7 +298,9 @@ static inline void __vmpclear(u64 addr)
     asm volatile ( VMCLEAR_OPCODE
                    MODRM_EAX_06
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 1f ; ud2 ; 1:\n"
+                   UNLIKELY_START(be, vmclear)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION
                    :
                    : "a" (&addr)
                    : "memory");
@@ -309,7 +313,9 @@ static inline unsigned long __vmread(uns
     asm volatile ( VMREAD_OPCODE
                    MODRM_EAX_ECX
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 1f ; ud2 ; 1:\n"
+                   UNLIKELY_START(be, vmread)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION
                    : "=c" (ecx)
                    : "a" (field)
                    : "memory");
@@ -322,7 +328,9 @@ static inline void __vmwrite(unsigned lo
     asm volatile ( VMWRITE_OPCODE
                    MODRM_EAX_ECX
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 1f ; ud2 ; 1:\n"
+                   UNLIKELY_START(be, vmwrite)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION
                    : 
                    : "a" (field) , "c" (value)
                    : "memory");
@@ -360,7 +368,9 @@ static inline void __invept(int type, u6
     asm volatile ( INVEPT_OPCODE
                    MODRM_EAX_08
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 1f ; ud2 ; 1:\n"
+                   UNLIKELY_START(be, invept)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION
                    :
                    : "a" (&operand), "c" (type)
                    : "memory" );
@@ -377,7 +387,10 @@ static inline void __invvpid(int type, u
     /* Fix up #UD exceptions which occur when TLBs are flushed before VMXON. */
     asm volatile ( "1: " INVVPID_OPCODE MODRM_EAX_08
                    /* CF==1 or ZF==1 --> crash (ud2) */
-                   "ja 2f ; ud2 ; 2:\n"
+                   UNLIKELY_START(be, invvpid)
+                   "\tud2\n"
+                   UNLIKELY_END_SECTION "\n"
+                   "2:"
                    _ASM_EXTABLE(1b, 2b)
                    :
                    : "a" (&operand), "c" (type)

Attachment: VMX-ud2-out-of-line.patch
Description: Text document

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