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[PATCH v5 5/5] x86/hvm: Un-indent the HVM_FEP block in the #UD handler


  • To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
  • Date: Thu, 12 Mar 2026 12:21:14 +0100
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  • Cc: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 12 Mar 2026 11:21:58 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

FEP is now the only reason for the #UD handler to run.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 43 +++++++++++++++++++++---------------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index c8cae41705d..4c00cf4c4fe 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3837,35 +3837,34 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
     struct vcpu *cur = current;
     bool should_emulate = false;
     struct hvm_emulate_ctxt ctxt;
+    const struct segment_register *cs;
+    uint32_t walk;
+    unsigned long addr;
+    char sig[5]; /* ud2; .ascii "xen" */
 
     hvm_emulate_init_once(&ctxt, NULL, regs);
 
-    if ( opt_hvm_fep )
+    cs = &ctxt.seg_reg[x86_seg_cs];
+    walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3)
+            ? PFEC_user_mode : 0) | PFEC_insn_fetch;
+
+    if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip,
+                                    sizeof(sig), hvm_access_insn_fetch,
+                                    cs, &addr) &&
+         (hvm_copy_from_guest_linear(sig, addr, sizeof(sig),
+                                     walk, NULL) == HVMTRANS_okay) &&
+         (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) )
     {
-        const struct segment_register *cs = &ctxt.seg_reg[x86_seg_cs];
-        uint32_t walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3)
-                         ? PFEC_user_mode : 0) | PFEC_insn_fetch;
-        unsigned long addr;
-        char sig[5]; /* ud2; .ascii "xen" */
-
-        if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip,
-                                        sizeof(sig), hvm_access_insn_fetch,
-                                        cs, &addr) &&
-             (hvm_copy_from_guest_linear(sig, addr, sizeof(sig),
-                                         walk, NULL) == HVMTRANS_okay) &&
-             (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) )
-        {
-            regs->rip += sizeof(sig);
-            regs->eflags &= ~X86_EFLAGS_RF;
+        regs->rip += sizeof(sig);
+        regs->eflags &= ~X86_EFLAGS_RF;
 
-            /* Zero the upper 32 bits of %rip if not in 64bit mode. */
-            if ( !(hvm_long_mode_active(cur) && cs->l) )
-                regs->rip = (uint32_t)regs->rip;
+        /* Zero the upper 32 bits of %rip if not in 64bit mode. */
+        if ( !(hvm_long_mode_active(cur) && cs->l) )
+            regs->rip = (uint32_t)regs->rip;
 
-            add_taint(TAINT_HVM_FEP);
+        add_taint(TAINT_HVM_FEP);
 
-            should_emulate = true;
-        }
+        should_emulate = true;
     }
 
     if ( !should_emulate )
-- 
2.43.0




 


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