Revert "KVM: X86 emulator: fix source operand decoding for 8bit mov[zs]x instructions"

This reverts commit 5b5b3058, which was
commit 660696d1 upstream.

Paul Gortmaker <paul.gortmaker@windriver.com> writes:

[this patch] introduces the following:

arch/x86/kvm/emulate.c: In function ‘decode_operand’:
arch/x86/kvm/emulate.c:3974:4: warning: passing argument 1 of ‘decode_register’ makes integer from pointer
+without a cast [enabled by default]
arch/x86/kvm/emulate.c:789:14: note: expected ‘u8’ but argument is of type ‘struct x86_emulate_ctxt *’
arch/x86/kvm/emulate.c:3974:4: warning: passing argument 2 of ‘decode_register’ makes pointer from integer
+without a cast [enabled by default]
arch/x86/kvm/emulate.c:789:14: note: expected ‘long unsigned int *’ but argument is of type ‘u8’

Based on the severity of the warnings above, I'm reasonably sure there will
be some kind of runtime regressions due to this, but I stopped to investigate
the warnings as soon as I saw them, before any run time testing.

It happens because mainline v3.7-rc1~113^2~40 (dd856efa) does this:

-static void *decode_register(u8 modrm_reg, unsigned long *regs,
+static void *decode_register(struct x86_emulate_ctxt *ctxt, u8 modrm_reg,

Since 660696d1 was only applied to stable 3.4, 3.8, and 3.9 -- and
the prerequisite above is in 3.7+, the issue should be limited to 3.4.44+
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kvm/emulate.c

@@ -3737,10 +3737,6 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
 		break;
 	case OpMem8:
 		ctxt->memop.bytes = 1;
-		if (ctxt->memop.type == OP_REG) {
-			ctxt->memop.addr.reg = decode_register(ctxt, ctxt->modrm_rm, 1);
-			fetch_register_operand(&ctxt->memop);
-		}
 		goto mem_common;
 	case OpMem16:
 		ctxt->memop.bytes = 2;