[PATCH] target/i386: allow MMX instructions with CR4.OSFXSR=0

[Paolo Bonzini <pbonzini@redhat.com>]

MMX state is saved/restored by FSAVE/FRSTOR so the instructions are
not illegal opcodes even if CR4.OSFXSR=0.  Make sure that validate_vex
takes into account the prefix and only checks HF_OSFXSR_MASK in the
presence of an SSE instruction.

Fixes: 20581aadec5e ("target/i386: validate VEX prefixes via the instructions' exception classes", 2022-10-18)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1350
Reported-by: Helge Konetzka (@hejko on gitlab.com)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/decode-new.c.inc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
index e4878b967f0e..80c579164ff2 100644
--- a/target/i386/tcg/decode-new.c.inc
+++ b/target/i386/tcg/decode-new.c.inc
@@ -1488,7 +1488,8 @@ static bool validate_vex(DisasContext *s, X86DecodedInsn *decode)
             if (!(s->flags & HF_AVX_EN_MASK)) {
                 goto illegal;
             }
-        } else {
+        } else if (e->special != X86_SPECIAL_MMX ||
+                   (s->prefix & (PREFIX_REPZ | PREFIX_REPNZ | PREFIX_DATA))) {
             if (!(s->flags & HF_OSFXSR_MASK)) {
                 goto illegal;
             }
-- 
2.38.1