Commit b4c6abfe authored by Laurent Vivier's avatar Laurent Vivier Committed by Avi Kivity
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KVM: x86 emulator: Any legacy prefix after a REX prefix nullifies its effect 

This patch modifies the management of REX prefix according behavior
I saw in Xen 3.1.  In Xen, this modification has been introduced by
Jan Beulich.

http://lists.xensource.com/archives/html/xen-changelog/2007-01/msg00081.html



Signed-off-by: default avatarLaurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent a22436b7

drivers/kvm/x86_emulate.c

+15 −9
Original line number Diff line number Diff line
@@ -521,7 +521,6 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
{

	struct decode_cache *c = &ctxt->decode;

	u8 sib, rex_prefix = 0;

	unsigned int i;

	int rc = 0;

	int mode = ctxt->mode;

	int index_reg = 0, base_reg = 0, scale, rip_relative = 0;
@@ -551,7 +550,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
	}



	/* Legacy prefixes. */

	for (i = 0; i < 8; i++) {

	for (;;) {

		switch (c->b = insn_fetch(u8, 1, c->eip)) {

		case 0x66:	/* operand-size override */

			c->op_bytes ^= 6;	/* switch between 2/4 bytes */
@@ -582,6 +581,11 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
		case 0x36:	/* SS override */

			c->override_base = &ctxt->ss_base;

			break;

		case 0x40 ... 0x4f: /* REX */

			if (mode != X86EMUL_MODE_PROT64)

				goto done_prefixes;

			rex_prefix = c->b;

			continue;

		case 0xf0:	/* LOCK */

			c->lock_prefix = 1;

			break;
@@ -592,19 +596,21 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
		default:

			goto done_prefixes;

		}



		/* Any legacy prefix after a REX prefix nullifies its effect. */



		rex_prefix = 0;

	}



done_prefixes:



	/* REX prefix. */

	if ((mode == X86EMUL_MODE_PROT64) && ((c->b & 0xf0) == 0x40)) {

		rex_prefix = c->b;

		if (c->b & 8)

	if (rex_prefix) {

		if (rex_prefix & 8)

			c->op_bytes = 8;	/* REX.W */

		c->modrm_reg = (c->b & 4) << 1;	/* REX.R */

		index_reg = (c->b & 2) << 2; /* REX.X */

		c->modrm_rm = base_reg = (c->b & 1) << 3; /* REG.B */

		c->b = insn_fetch(u8, 1, c->eip);

		c->modrm_reg = (rex_prefix & 4) << 1;	/* REX.R */

		index_reg = (rex_prefix & 2) << 2; /* REX.X */

		c->modrm_rm = base_reg = (rex_prefix & 1) << 3; /* REG.B */

	}



	/* Opcode byte(s). */