[PATCH] x86/shadow: suppress trace_emul_write_val hook when !TRACEBUFFER

[Jan Beulich <jbeulich@xxxxxxxx>]

The hook is never invoked in that case, and hence needlessly offers an
extra valid indirect call target. With the hook suppressed, no consumer
of the three local per-CPU variables exists either, so they're
suppressed as well.

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

--- a/xen/arch/x86/include/asm/paging.h
+++ b/xen/arch/x86/include/asm/paging.h
@@ -90,10 +90,12 @@ struct shadow_paging_mode {
     int           (*guess_wrmap           )(struct vcpu *v, 
                                             unsigned long vaddr, mfn_t gmfn);
     void          (*pagetable_dying       )(paddr_t gpa);
+#ifdef CONFIG_TRACEBUFFER
     void          (*trace_emul_write_val  )(const void *ptr, unsigned long 
vaddr,
                                             const void *src, unsigned int 
bytes);
 #endif
 #endif
+#endif
     /* For outsiders to tell what mode we're in */
     unsigned int shadow_levels;
 };
--- a/xen/arch/x86/mm/shadow/hvm.c
+++ b/xen/arch/x86/mm/shadow/hvm.c
@@ -211,9 +211,11 @@ hvm_emulate_write(enum x86_segment seg,
     default: memcpy(ptr, p_data, bytes);                break;
     }
 
+#ifdef CONFIG_TRACEBUFFER
     if ( tb_init_done )
         v->arch.paging.mode->shadow.trace_emul_write_val(ptr, addr,
                                                          p_data, bytes);
+#endif
 
     sh_emulate_unmap_dest(v, ptr, bytes, sh_ctxt);
     shadow_audit_tables(v);
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -2044,6 +2044,7 @@ static void __maybe_unused sh_trace_gfn_
 }
 
 #ifdef CONFIG_HVM
+#ifdef CONFIG_TRACEBUFFER
 #if GUEST_PAGING_LEVELS == 3
 static DEFINE_PER_CPU(guest_va_t,trace_emulate_initial_va);
 static DEFINE_PER_CPU(int,trace_extra_emulation_count);
@@ -2071,9 +2072,11 @@ static void cf_check trace_emulate_write
     memcpy(&this_cpu(trace_emulate_write_val), src, bytes);
 #endif
 }
+#endif /* CONFIG_TRACEBUFFER */
 
 static inline void sh_trace_emulate(guest_l1e_t gl1e, unsigned long va)
 {
+#ifdef CONFIG_TRACEBUFFER
     if ( tb_init_done )
     {
         struct __packed {
@@ -2099,6 +2102,7 @@ static inline void sh_trace_emulate(gues
 
         sh_trace(TRC_SHADOW_EMULATE, sizeof(d), &d);
     }
+#endif /* CONFIG_TRACEBUFFER */
 }
 #endif /* CONFIG_HVM */
 
@@ -2678,7 +2682,9 @@ static int cf_check sh_page_fault(
     paging_unlock(d);
     put_gfn(d, gfn_x(gfn));
 
+#ifdef CONFIG_TRACEBUFFER
     this_cpu(trace_emulate_write_val) = (guest_l1e_t){};
+#endif
 
 #if SHADOW_OPTIMIZATIONS & SHOPT_FAST_EMULATION
  early_emulation:
@@ -2794,7 +2800,10 @@ static int cf_check sh_page_fault(
     if ( r == X86EMUL_OKAY && !emul_ctxt.ctxt.retire.raw )
     {
         int i, emulation_count=0;
+
+#ifdef CONFIG_TRACEBUFFER
         this_cpu(trace_emulate_initial_va) = va;
+#endif
 
         for ( i = 0 ; i < 4 ; i++ )
         {
@@ -2830,7 +2839,10 @@ static int cf_check sh_page_fault(
                 break; /* Don't emulate again if we failed! */
             }
         }
+
+#ifdef CONFIG_TRACEBUFFER
         this_cpu(trace_extra_emulation_count)=emulation_count;
+#endif
     }
 #endif /* PAE guest */
 
@@ -4130,7 +4142,9 @@ const struct paging_mode sh_paging_mode
     .shadow.guess_wrmap            = sh_guess_wrmap,
 #endif
     .shadow.pagetable_dying        = sh_pagetable_dying,
+#ifdef CONFIG_TRACEBUFFER
     .shadow.trace_emul_write_val   = trace_emulate_write_val,
+#endif
 #endif /* CONFIG_HVM */
     .shadow.shadow_levels          = SHADOW_PAGING_LEVELS,
 };