x86emul: support {,V}{,U}COMIS{S,D}

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Add missing RET to stub. Generate #UD (instead of simply failing)
    when VEX.l is disallowed.

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -249,7 +249,7 @@ static const struct {
     [0x2a] = { DstImplicit|SrcMem|ModRM|Mov, simd_other },
     [0x2b] = { DstMem|SrcImplicit|ModRM|Mov, simd_any_fp },
     [0x2c ... 0x2d] = { DstImplicit|SrcMem|ModRM|Mov, simd_other },
-    [0x2e ... 0x2f] = { ImplicitOps|ModRM },
+    [0x2e ... 0x2f] = { ImplicitOps|ModRM|TwoOp },
     [0x30 ... 0x35] = { ImplicitOps },
     [0x37] = { ImplicitOps },
     [0x38] = { DstReg|SrcMem|ModRM },
@@ -5485,6 +5485,54 @@ x86_emulate(
         state->simd_size = simd_none;
         break;
 
+    CASE_SIMD_PACKED_FP(, 0x0f, 0x2e):     /* ucomis{s,d} xmm/mem,xmm */
+    CASE_SIMD_PACKED_FP(_VEX, 0x0f, 0x2e): /* vucomis{s,d} xmm/mem,xmm */
+    CASE_SIMD_PACKED_FP(, 0x0f, 0x2f):     /* comis{s,d} xmm/mem,xmm */
+    CASE_SIMD_PACKED_FP(_VEX, 0x0f, 0x2f): /* vcomis{s,d} xmm/mem,xmm */
+        if ( vex.opcx == vex_none )
+        {
+            if ( vex.pfx )
+                vcpu_must_have(sse2);
+            else
+                vcpu_must_have(sse);
+            get_fpu(X86EMUL_FPU_xmm, &fic);
+        }
+        else
+        {
+            generate_exception_if(vex.l || vex.reg != 0xf, EXC_UD);
+            host_and_vcpu_must_have(avx);
+            get_fpu(X86EMUL_FPU_ymm, &fic);
+        }
+
+        opc = init_prefixes(stub);
+        opc[0] = b;
+        opc[1] = modrm;
+        if ( ea.type == OP_MEM )
+        {
+            rc = ops->read(ea.mem.seg, ea.mem.off, mmvalp, vex.pfx ? 8 : 4,
+                           ctxt);
+            if ( rc != X86EMUL_OKAY )
+                goto done;
+
+            /* Convert memory operand to (%rAX). */
+            rex_prefix &= ~REX_B;
+            vex.b = 1;
+            opc[1] &= 0x38;
+        }
+        fic.insn_bytes = PFX_BYTES + 2;
+        opc[2] = 0xc3;
+
+        invoke_stub(_PRE_EFLAGS("[eflags]", "[mask]", "[tmp]"),
+                    _POST_EFLAGS("[eflags]", "[mask]", "[tmp]"),
+                    [eflags] "+g" (_regs._eflags),
+                    [tmp] "=&r" (cr4), "+m" (*mmvalp)
+                    : [func] "rm" (stub.func), "a" (mmvalp),
+                      [mask] "i" (EFLAGS_MASK));
+
+        put_stub(stub);
+        put_fpu(&fic);
+        break;
+
     case X86EMUL_OPC(0x0f, 0x30): /* wrmsr */
         generate_exception_if(!mode_ring0(), EXC_GP, 0);
         fail_if(ops->write_msr == NULL);