[Xen-devel] [PATCH 1/2] x86emul: fix vector-length check for AVX512F scalar fused-multiply-add insns

["Jan Beulich" <JBeulich@xxxxxxxx>]

The check needs to happen whenever EVEX.b is clear, not just in the
memory operand case.

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

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -8526,11 +8526,9 @@ x86_emulate(
     case X86EMUL_OPC_EVEX_66(0x0f38, 0xbd): /* vfnmadd231s{s,d} 
xmm/mem,xmm,xmm{k} */
     case X86EMUL_OPC_EVEX_66(0x0f38, 0xbf): /* vfnmsub231s{s,d} 
xmm/mem,xmm,xmm{k} */
         host_and_vcpu_must_have(avx512f);
-        if ( ea.type == OP_MEM )
-        {
-            generate_exception_if(evex.br, EXC_UD);
+        generate_exception_if(ea.type != OP_REG && evex.br, EXC_UD);
+        if ( !evex.br )
             avx512_vlen_check(true);
-        }
         goto simd_zmm;
 
     case X86EMUL_OPC(0x0f38, 0xc8):     /* sha1nexte xmm/m128,xmm */



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