VMX: fix/adjust trap injection

In the course of investigating the 4.1.6 backport issue of the XSA-156
patch I realized that #DB injection has always been broken, but with it
now getting always intercepted the problem has got worse: Documentation
clearly states that neither DR7.GD nor DebugCtl.LBR get cleared before
the intercept, so this is something we need to do before reflecting the
intercepted exception.

While adjusting this (and also with 4.1.6's strange use of
X86_EVENTTYPE_SW_EXCEPTION for #DB in mind) I further realized that
the special casing of individual vectors shouldn't be done for
software interrupts (resulting from INT $nn).

And then some code movement: Setting of CR2 for #PF can be done in the
same switch() statement (no need for a separate if()), and reading of
intr_info is better done close the the consumption of the variable
(allowing the compiler to generate better code / use fewer registers
for variables).

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

--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1508,16 +1508,7 @@ static void vmx_inject_trap(struct hvm_t
     struct vcpu *curr = current;
     struct hvm_trap _trap = *trap;
 
-    if ( (_trap.vector == TRAP_page_fault) &&
-         (_trap.type == X86_EVENTTYPE_HW_EXCEPTION) )
-        curr->arch.hvm_vcpu.guest_cr[2] = _trap.cr2;
-
-    if ( nestedhvm_vcpu_in_guestmode(curr) )
-        intr_info = vcpu_2_nvmx(curr).intr.intr_info;
-    else
-        __vmread(VM_ENTRY_INTR_INFO, &intr_info);
-
-    switch ( _trap.vector )
+    switch ( _trap.vector | -(_trap.type == X86_EVENTTYPE_SW_INTERRUPT) )
     {
     case TRAP_debug:
         if ( guest_cpu_user_regs()->eflags & X86_EFLAGS_TF )
@@ -1525,6 +1516,16 @@ static void vmx_inject_trap(struct hvm_t
             __restore_debug_registers(curr);
             write_debugreg(6, read_debugreg(6) | DR_STEP);
         }
+        if ( !nestedhvm_vcpu_in_guestmode(curr) ||
+             !nvmx_intercepts_exception(curr, TRAP_debug, _trap.error_code) )
+        {
+            unsigned long val;
+
+            __vmread(GUEST_DR7, &val);
+            __vmwrite(GUEST_DR7, val & ~DR_GENERAL_DETECT);
+            __vmread(GUEST_IA32_DEBUGCTL, &val);
+            __vmwrite(GUEST_IA32_DEBUGCTL, val & ~IA32_DEBUGCTLMSR_LBR);
+        }
         if ( cpu_has_monitor_trap_flag )
             break;
         /* fall through */
@@ -1535,8 +1536,19 @@ static void vmx_inject_trap(struct hvm_t
             domain_pause_for_debugger();
             return;
         }
+        break;
+
+    case TRAP_page_fault:
+        ASSERT(_trap.type == X86_EVENTTYPE_HW_EXCEPTION);
+        curr->arch.hvm_vcpu.guest_cr[2] = _trap.cr2;
+        break;
     }
 
+    if ( nestedhvm_vcpu_in_guestmode(curr) )
+        intr_info = vcpu_2_nvmx(curr).intr.intr_info;
+    else
+        __vmread(VM_ENTRY_INTR_INFO, &intr_info);
+
     if ( unlikely(intr_info & INTR_INFO_VALID_MASK) &&
          (MASK_EXTR(intr_info, INTR_INFO_INTR_TYPE_MASK) ==
           X86_EVENTTYPE_HW_EXCEPTION) )