[PATCH 2/4] x86/hvm: Disable non-FEP cross-vendor handling in #UD handler

[Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>]

Remove cross-vendor support now that VMs can no longer have a different
vendor than the host, leaving FEP as the sole raison-d'être for #UD
interception.

Not a functional change.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c     | 25 ++++---------------------
 xen/arch/x86/hvm/svm/svm.c |  4 ++--
 xen/arch/x86/hvm/vmx/vmx.c |  4 ++--
 3 files changed, 8 insertions(+), 25 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 4d37a93c57..611ff83a60 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3832,28 +3832,13 @@ int hvm_descriptor_access_intercept(uint64_t exit_info,
     return X86EMUL_OKAY;
 }
 
-static bool cf_check is_cross_vendor(
-    const struct x86_emulate_state *state, const struct x86_emulate_ctxt *ctxt)
-{
-    switch ( ctxt->opcode )
-    {
-    case X86EMUL_OPC(0x0f, 0x05): /* syscall */
-    case X86EMUL_OPC(0x0f, 0x34): /* sysenter */
-    case X86EMUL_OPC(0x0f, 0x35): /* sysexit */
-        return true;
-    }
-
-    return false;
-}
-
+#ifdef CONFIG_HVM_FEP
 void hvm_ud_intercept(struct cpu_user_regs *regs)
 {
     struct vcpu *cur = current;
-    bool should_emulate =
-        cur->domain->arch.cpuid->x86_vendor != boot_cpu_data.x86_vendor;
     struct hvm_emulate_ctxt ctxt;
 
-    hvm_emulate_init_once(&ctxt, opt_hvm_fep ? NULL : is_cross_vendor, regs);
+    hvm_emulate_init_once(&ctxt, NULL, regs);
 
     if ( opt_hvm_fep )
     {
@@ -3878,12 +3863,9 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
                 regs->rip = (uint32_t)regs->rip;
 
             add_taint(TAINT_HVM_FEP);
-
-            should_emulate = true;
         }
     }
-
-    if ( !should_emulate )
+    else
     {
         hvm_inject_hw_exception(X86_EXC_UD, X86_EVENT_NO_EC);
         return;
@@ -3903,6 +3885,7 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
         break;
     }
 }
+#endif /* CONFIG_HVM_FEP */
 
 enum hvm_intblk hvm_interrupt_blocked(struct vcpu *v, struct hvm_intack intack)
 {
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 18ba837738..0658ca990f 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -589,8 +589,7 @@ static void cf_check svm_cpuid_policy_changed(struct vcpu 
*v)
     const struct cpu_policy *cp = v->domain->arch.cpu_policy;
     u32 bitmap = vmcb_get_exception_intercepts(vmcb);
 
-    if ( opt_hvm_fep ||
-         (v->domain->arch.cpuid->x86_vendor != boot_cpu_data.x86_vendor) )
+    if ( opt_hvm_fep )
         bitmap |= (1U << X86_EXC_UD);
     else
         bitmap &= ~(1U << X86_EXC_UD);
@@ -2810,6 +2809,7 @@ void asmlinkage svm_vmexit_handler(void)
         break;
 
     case VMEXIT_EXCEPTION_UD:
+        BUG_ON(!IS_ENABLED(CONFIG_HVM_FEP));
         hvm_ud_intercept(regs);
         break;
 
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 40e4c71244..34e988ee61 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -797,8 +797,7 @@ static void cf_check vmx_cpuid_policy_changed(struct vcpu 
*v)
     const struct cpu_policy *cp = v->domain->arch.cpu_policy;
     int rc = 0;
 
-    if ( opt_hvm_fep ||
-         (v->domain->arch.cpuid->x86_vendor != boot_cpu_data.x86_vendor) )
+    if ( opt_hvm_fep )
         v->arch.hvm.vmx.exception_bitmap |= (1U << X86_EXC_UD);
     else
         v->arch.hvm.vmx.exception_bitmap &= ~(1U << X86_EXC_UD);
@@ -4576,6 +4575,7 @@ void asmlinkage vmx_vmexit_handler(struct cpu_user_regs 
*regs)
             /* Already handled above. */
             break;
         case X86_EXC_UD:
+            BUG_ON(!IS_ENABLED(CONFIG_HVM_FEP));
             TRACE(TRC_HVM_TRAP, vector);
             hvm_ud_intercept(regs);
             break;
-- 
2.43.0