[Xen-devel] [PATCH 1/3] x86/traps: Export the exception_table[] function pointer table to C

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

and use it in preference to the direct call to do_nmi() in vmx.c

The value 'TRAP_last_reserved' was only used where 'TRAP_nr' would be more
appropriate, so is replaced.

No functional change

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>

---
Diffing the dissassembly confirms no change:

 @@ -236036,10 +236036,10 @@
 ffff82d0801e1a9d:      48 3d 00 02 00 00       cmp    $0x200,%rax
 ffff82d0801e1aa3:      0f 85 84 fe ff ff       jne    ffff82d0801e192d 
<vmx_vmexit_handler+0x10d>
 ffff82d0801e1aa9:      48 89 ef                mov    %rbp,%rdi
-ffff82d0801e1aac:      e8 4f c3 fa ff          callq  ffff82d08018de00 <do_nmi>
-ffff82d0801e1ab1:      e8 ea 7f 04 00          callq  ffff82d080229aa0 
<enable_nmis>
-ffff82d0801e1ab6:      e9 72 fe ff ff          jmpq   ffff82d0801e192d 
<vmx_vmexit_handler+0x10d>
-ffff82d0801e1abb:      0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
+ffff82d0801e1aac:      ff 15 be 62 05 00       callq  *0x562be(%rip)
+ffff82d0801e1ab2:      e8 e9 7f 04 00          callq  ffff82d080229aa0 
<enable_nmis>
+ffff82d0801e1ab7:      e9 71 fe ff ff          jmpq   ffff82d0801e192d 
<vmx_vmexit_handler+0x10d>
+ffff82d0801e1abc:      0f 1f 40 00             nopl   0x0(%rax)
 ffff82d0801e1ac0:      f6 83 c3 03 00 00 80    testb  $0x80,0x3c3(%rbx)
 ffff82d0801e1ac7:      0f 84 07 fe ff ff       je     ffff82d0801e18d4 
<vmx_vmexit_handler+0xb4>
 ffff82d0801e1acd:      48 8b 83 08 04 00 00    mov    0x408(%rbx),%rax
---
 xen/arch/x86/hvm/vmx/vmx.c      |    2 +-
 xen/arch/x86/x86_64/entry.S     |    5 +++--
 xen/include/asm-x86/processor.h |    5 ++++-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 88b7821..357ef6c 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2701,7 +2701,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
              && ((intr_info & INTR_INFO_INTR_TYPE_MASK) ==
                  (X86_EVENTTYPE_NMI << 8)) )
         {
-            do_nmi(regs);
+            exception_table[TRAP_nmi](regs);
             enable_nmis();
         }
         break;
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index b3d6e32..062c690 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -728,9 +728,10 @@ ENTRY(exception_table)
         .quad do_alignment_check
         .quad do_machine_check
         .quad do_simd_coprocessor_error
-        .rept TRAP_last_reserved + 1 - ((. - exception_table) / 8)
+        .rept TRAP_nr - ((. - exception_table) / 8)
         .quad do_reserved_trap /* Architecturally reserved exceptions. */
         .endr
+        .size exception_table, . - exception_table
 
 ENTRY(hypercall_table)
         .quad do_set_trap_table     /*  0 */
@@ -857,7 +858,7 @@ autogen_stubs: /* Automatically generated stubs. */
         entrypoint 1b
 
         /* Reserved exceptions, heading towards do_reserved_trap(). */
-        .elseif vec == TRAP_copro_seg || vec == TRAP_spurious_int || (vec > 
TRAP_simd_error && vec <= TRAP_last_reserved)
+        .elseif vec == TRAP_copro_seg || vec == TRAP_spurious_int || (vec > 
TRAP_simd_error && vec < TRAP_nr)
 
 1:      test  $8,%spl        /* 64bit exception frames are 16 byte aligned, 
but the word */
         jz    2f             /* size is 8 bytes.  Check whether the processor 
gave us an */
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index 20eade6..2773ea8 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -114,7 +114,7 @@
 #define TRAP_machine_check    18
 #define TRAP_simd_error       19
 #define TRAP_virtualisation   20
-#define TRAP_last_reserved    31
+#define TRAP_nr               32
 
 /* Set for entry via SYSCALL. Informs return code to use SYSRETQ not IRETQ. */
 /* NB. Same as VGCF_in_syscall. No bits in common with any other TRAP_ defn. */
@@ -492,6 +492,9 @@ extern void mtrr_bp_init(void);
 
 void mcheck_init(struct cpuinfo_x86 *c, bool_t bsp);
 
+/* Dispatch table for exceptions */
+extern void (* const exception_table[TRAP_nr])(struct cpu_user_regs *regs);
+
 #define DECLARE_TRAP_HANDLER(_name)                    \
     void _name(void);                                  \
     void do_ ## _name(struct cpu_user_regs *regs)
-- 
1.7.10.4


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