x86/HVM: unify and fix #UD intercept

The SVM and VMX versions really were identical, so instead of fixing
the same issue in two places, fold them at once. The issue fixed is the
missing seg:off -> linear translation of the current code address.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -92,9 +92,12 @@ unsigned long __section(".bss.page_align
 static bool_t __initdata opt_hap_enabled = 1;
 boolean_param("hap", opt_hap_enabled);
 
-#ifndef opt_hvm_fep
-bool_t opt_hvm_fep;
+#ifndef NDEBUG
+/* Permit use of the Forced Emulation Prefix in HVM guests */
+static bool_t opt_hvm_fep;
 boolean_param("hvm_fep", opt_hvm_fep);
+#else
+#define opt_hvm_fep 0
 #endif
 
 /* Xen command-line option to enable altp2m */
@@ -4931,6 +4934,49 @@ gp_fault:
     return X86EMUL_EXCEPTION;
 }
 
+void hvm_ud_intercept(struct cpu_user_regs *regs)
+{
+    struct hvm_emulate_ctxt ctxt;
+
+    if ( opt_hvm_fep )
+    {
+        struct vcpu *cur = current;
+        struct segment_register cs;
+        unsigned long addr;
+        char sig[5]; /* ud2; .ascii "xen" */
+
+        hvm_get_segment_register(cur, x86_seg_cs, &cs);
+        if ( hvm_virtual_to_linear_addr(x86_seg_cs, &cs, regs->eip,
+                                        sizeof(sig), hvm_access_insn_fetch,
+                                        (hvm_long_mode_enabled(cur) &&
+                                         cs.attr.fields.l) ? 64 :
+                                        cs.attr.fields.db ? 32 : 16, &addr) &&
+             (hvm_fetch_from_guest_virt_nofault(sig, addr, sizeof(sig),
+                                                0) == HVMCOPY_okay) &&
+             (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
+        {
+            regs->eip += sizeof(sig);
+            regs->eflags &= ~X86_EFLAGS_RF;
+        }
+    }
+
+    hvm_emulate_prepare(&ctxt, regs);
+
+    switch ( hvm_emulate_one(&ctxt) )
+    {
+    case X86EMUL_UNHANDLEABLE:
+        hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
+        break;
+    case X86EMUL_EXCEPTION:
+        if ( ctxt.exn_pending )
+            hvm_inject_trap(&ctxt.trap);
+        /* fall through */
+    default:
+        hvm_emulate_writeback(&ctxt);
+        break;
+    }
+}
+
 enum hvm_intblk hvm_interrupt_blocked(struct vcpu *v, struct hvm_intack intack)
 {
     unsigned long intr_shadow;
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2123,43 +2123,6 @@ svm_vmexit_do_vmsave(struct vmcb_struct
     return;
 }
 
-static void svm_vmexit_ud_intercept(struct cpu_user_regs *regs)
-{
-    struct hvm_emulate_ctxt ctxt;
-    int rc;
-
-    if ( opt_hvm_fep )
-    {
-        char sig[5]; /* ud2; .ascii "xen" */
-
-        if ( (hvm_fetch_from_guest_virt_nofault(
-                  sig, regs->eip, sizeof(sig), 0) == HVMCOPY_okay) &&
-             (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
-        {
-            regs->eip += sizeof(sig);
-            regs->eflags &= ~X86_EFLAGS_RF;
-        }
-    }
-
-    hvm_emulate_prepare(&ctxt, regs);
-
-    rc = hvm_emulate_one(&ctxt);
-
-    switch ( rc )
-    {
-    case X86EMUL_UNHANDLEABLE:
-        hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
-        break;
-    case X86EMUL_EXCEPTION:
-        if ( ctxt.exn_pending )
-            hvm_inject_trap(&ctxt.trap);
-        /* fall through */
-    default:
-        hvm_emulate_writeback(&ctxt);
-        break;
-    }
-}
-
 static int svm_is_erratum_383(struct cpu_user_regs *regs)
 {
     uint64_t msr_content;
@@ -2491,7 +2454,7 @@ void svm_vmexit_handler(struct cpu_user_
         break;
 
     case VMEXIT_EXCEPTION_UD:
-        svm_vmexit_ud_intercept(regs);
+        hvm_ud_intercept(regs);
         break;
 
     /* Asynchronous event, handled when we STGI'd after the VMEXIT. */
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2747,43 +2747,6 @@ void vmx_enter_realmode(struct cpu_user_
     regs->eflags |= (X86_EFLAGS_VM | X86_EFLAGS_IOPL);
 }
 
-static void vmx_vmexit_ud_intercept(struct cpu_user_regs *regs)
-{
-    struct hvm_emulate_ctxt ctxt;
-    int rc;
-
-    if ( opt_hvm_fep )
-    {
-        char sig[5]; /* ud2; .ascii "xen" */
-
-        if ( (hvm_fetch_from_guest_virt_nofault(
-                  sig, regs->eip, sizeof(sig), 0) == HVMCOPY_okay) &&
-             (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
-        {
-            regs->eip += sizeof(sig);
-            regs->eflags &= ~X86_EFLAGS_RF;
-        }
-    }
-
-    hvm_emulate_prepare(&ctxt, regs);
-
-    rc = hvm_emulate_one(&ctxt);
-
-    switch ( rc )
-    {
-    case X86EMUL_UNHANDLEABLE:
-        hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
-        break;
-    case X86EMUL_EXCEPTION:
-        if ( ctxt.exn_pending )
-            hvm_inject_trap(&ctxt.trap);
-        /* fall through */
-    default:
-        hvm_emulate_writeback(&ctxt);
-        break;
-    }
-}
-
 static int vmx_handle_eoi_write(void)
 {
     unsigned long exit_qualification;
@@ -3138,7 +3101,7 @@ void vmx_vmexit_handler(struct cpu_user_
             break;
         case TRAP_invalid_op:
             HVMTRACE_1D(TRAP, vector);
-            vmx_vmexit_ud_intercept(regs);
+            hvm_ud_intercept(regs);
             break;
         default:
             HVMTRACE_1D(TRAP, vector);
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -551,13 +551,6 @@ static inline bool_t hvm_altp2m_supporte
     return hvm_funcs.altp2m_supported;
 }
 
-#ifndef NDEBUG
-/* Permit use of the Forced Emulation Prefix in HVM guests */
-extern bool_t opt_hvm_fep;
-#else
-#define opt_hvm_fep 0
-#endif
-
 /* updates the current hardware p2m */
 void altp2m_vcpu_update_p2m(struct vcpu *v);
 
--- a/xen/include/asm-x86/hvm/support.h
+++ b/xen/include/asm-x86/hvm/support.h
@@ -131,6 +131,7 @@ int hvm_msr_write_intercept(
     unsigned int msr, uint64_t msr_content, bool_t may_defer);
 int hvm_mov_to_cr(unsigned int cr, unsigned int gpr);
 int hvm_mov_from_cr(unsigned int cr, unsigned int gpr);
+void hvm_ud_intercept(struct cpu_user_regs *);
 
 #endif /* __ASM_X86_HVM_SUPPORT_H__ */