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

[patchbot@xxxxxxx]

commit afdf0bc854f462995af5abec7fdd53cd9d310574
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jan 29 09:52:30 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 29 09:52:30 2026 +0100

    x86/shadow: suppress trace_emul_write_val hook when !TRACEBUFFER
    
    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>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/include/asm/paging.h |  6 ++++--
 xen/arch/x86/mm/shadow/hvm.c      |  2 ++
 xen/arch/x86/mm/shadow/multi.c    | 14 ++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/include/asm/paging.h 
b/xen/arch/x86/include/asm/paging.h
index 72d7c077e4..9668deed4c 100644
--- 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 /* CONFIG_TRACEBUFFER */
+#endif /* CONFIG_HVM */
+#endif /* CONFIG_SHADOW_PAGING */
     /* For outsiders to tell what mode we're in */
     unsigned int shadow_levels;
 };
diff --git a/xen/arch/x86/mm/shadow/hvm.c b/xen/arch/x86/mm/shadow/hvm.c
index 69334c0956..d857b1d9d6 100644
--- 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);
diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index e24ef0686f..72f0c6fcbc 100644
--- 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_va(uint32_t 
event, gfn_t 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_val(
     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(guest_l1e_t gl1e, 
unsigned long va)
 
         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 /* CONFIG_TRACEBUFFER */
 #endif /* CONFIG_HVM */
     .shadow.shadow_levels          = SHADOW_PAGING_LEVELS,
 };
--
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