Commit 62bd430e authored by Mohammed Gamal's avatar Mohammed Gamal Committed by Avi Kivity
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KVM: x86 emulator: Add IRET instruction 



Ths patch adds IRET instruction (opcode 0xcf).
Currently, only IRET in real mode is emulated. Protected mode support is to be added later if needed.

Signed-off-by: default avatarMohammed Gamal <m.gamal005@gmail.com>
Reviewed-by: default avatarAvi Kivity <avi@redhat.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent 7a190667

arch/x86/kvm/emulate.c

+81 −0
Original line number Diff line number Diff line
@@ -341,6 +341,9 @@ static u32 group2_table[] = { 
#define EFLG_PF (1<<2)

#define EFLG_CF (1<<0)



#define EFLG_RESERVED_ZEROS_MASK 0xffc0802a

#define EFLG_RESERVED_ONE_MASK 2



/*

 * Instruction emulation:

 * Most instructions are emulated directly via a fragment of inline assembly
@@ -1729,6 +1732,78 @@ static int emulate_popa(struct x86_emulate_ctxt *ctxt, 
	return rc;

}



static int emulate_iret_real(struct x86_emulate_ctxt *ctxt,

			     struct x86_emulate_ops *ops)

{

	struct decode_cache *c = &ctxt->decode;

	int rc = X86EMUL_CONTINUE;

	unsigned long temp_eip = 0;

	unsigned long temp_eflags = 0;

	unsigned long cs = 0;

	unsigned long mask = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF | EFLG_TF |

			     EFLG_IF | EFLG_DF | EFLG_OF | EFLG_IOPL | EFLG_NT | EFLG_RF |

			     EFLG_AC | EFLG_ID | (1 << 1); /* Last one is the reserved bit */

	unsigned long vm86_mask = EFLG_VM | EFLG_VIF | EFLG_VIP;



	/* TODO: Add stack limit check */



	rc = emulate_pop(ctxt, ops, &temp_eip, c->op_bytes);



	if (rc != X86EMUL_CONTINUE)

		return rc;



	if (temp_eip & ~0xffff) {

		emulate_gp(ctxt, 0);

		return X86EMUL_PROPAGATE_FAULT;

	}



	rc = emulate_pop(ctxt, ops, &cs, c->op_bytes);



	if (rc != X86EMUL_CONTINUE)

		return rc;



	rc = emulate_pop(ctxt, ops, &temp_eflags, c->op_bytes);



	if (rc != X86EMUL_CONTINUE)

		return rc;



	rc = load_segment_descriptor(ctxt, ops, (u16)cs, VCPU_SREG_CS);



	if (rc != X86EMUL_CONTINUE)

		return rc;



	c->eip = temp_eip;





	if (c->op_bytes == 4)

		ctxt->eflags = ((temp_eflags & mask) | (ctxt->eflags & vm86_mask));

	else if (c->op_bytes == 2) {

		ctxt->eflags &= ~0xffff;

		ctxt->eflags |= temp_eflags;

	}



	ctxt->eflags &= ~EFLG_RESERVED_ZEROS_MASK; /* Clear reserved zeros */

	ctxt->eflags |= EFLG_RESERVED_ONE_MASK;



	return rc;

}



static inline int emulate_iret(struct x86_emulate_ctxt *ctxt,

				    struct x86_emulate_ops* ops)

{

	switch(ctxt->mode) {

	case X86EMUL_MODE_REAL:

		return emulate_iret_real(ctxt, ops);

	case X86EMUL_MODE_VM86:

	case X86EMUL_MODE_PROT16:

	case X86EMUL_MODE_PROT32:

	case X86EMUL_MODE_PROT64:

	default:

		/* iret from protected mode unimplemented yet */

		return X86EMUL_UNHANDLEABLE;

	}

}



static inline int emulate_grp1a(struct x86_emulate_ctxt *ctxt,

				struct x86_emulate_ops *ops)

{
@@ -2857,6 +2932,12 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
		break;

	case 0xcb:		/* ret far */

		rc = emulate_ret_far(ctxt, ops);

		if (rc != X86EMUL_CONTINUE)

			goto done;

		break;

	case 0xcf:		/* iret */

		rc = emulate_iret(ctxt, ops);



		if (rc != X86EMUL_CONTINUE)

			goto done;

		break;