KVM: emulator: Use linearize() when fetching instructions

Since segments need to be handled slightly differently when fetching
instructions, we add a __linearize helper that accepts a new 'fetch' boolean.

[avi: fix oops caused by wrong segmented_address initialization order]
Signed-off-by: Nelson Elhage <nelhage@ksplice.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -265,7 +265,6 @@ struct x86_emulate_ctxt {
 	unsigned long eip; /* eip before instruction emulation */
 	/* Emulated execution mode, represented by an X86EMUL_MODE value. */
 	int mode;
-	u32 cs_base;
 
 	/* interruptibility state, as a result of execution of STI or MOV SS */
 	int interruptibility;

arch/x86/kvm/emulate.c

@@ -540,9 +540,9 @@ static int emulate_nm(struct x86_emulate_ctxt *ctxt)
 	return emulate_exception(ctxt, NM_VECTOR, 0, false);
 }
 
-static int linearize(struct x86_emulate_ctxt *ctxt,
+static int __linearize(struct x86_emulate_ctxt *ctxt,
 		     struct segmented_address addr,
-		     unsigned size, bool write,
+		     unsigned size, bool write, bool fetch,
 		     ulong *linear)
 {
 	struct decode_cache *c = &ctxt->decode;
@@ -569,7 +569,7 @@ static int linearize(struct x86_emulate_ctxt *ctxt,
 		if (((desc.type & 8) || !(desc.type & 2)) && write)
 			goto bad;
 		/* unreadable code segment */
-		if ((desc.type & 8) && !(desc.type & 2))
+		if (!fetch && (desc.type & 8) && !(desc.type & 2))
 			goto bad;
 		lim = desc_limit_scaled(&desc);
 		if ((desc.type & 8) || !(desc.type & 4)) {
@@ -602,7 +602,7 @@ static int linearize(struct x86_emulate_ctxt *ctxt,
 		}
 		break;
 	}
-	if (c->ad_bytes != 8)
+	if (fetch ? ctxt->mode != X86EMUL_MODE_PROT64 : c->ad_bytes != 8)
 		la &= (u32)-1;
 	*linear = la;
 	return X86EMUL_CONTINUE;
@@ -613,6 +613,15 @@ static int linearize(struct x86_emulate_ctxt *ctxt,
 		return emulate_gp(ctxt, addr.seg);
 }
 
+static int linearize(struct x86_emulate_ctxt *ctxt,
+		     struct segmented_address addr,
+		     unsigned size, bool write,
+		     ulong *linear)
+{
+	return __linearize(ctxt, addr, size, write, false, linear);
+}
+
+
 static int segmented_read_std(struct x86_emulate_ctxt *ctxt,
 			      struct segmented_address addr,
 			      void *data,
@@ -637,11 +646,13 @@ static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt,
 	int size, cur_size;
 
 	if (eip == fc->end) {
-		unsigned long linear = eip + ctxt->cs_base;
-		if (ctxt->mode != X86EMUL_MODE_PROT64)
-			linear &= (u32)-1;
+		unsigned long linear;
+		struct segmented_address addr = { .seg=VCPU_SREG_CS, .ea=eip};
 		cur_size = fc->end - fc->start;
 		size = min(15UL - cur_size, PAGE_SIZE - offset_in_page(eip));
+		rc = __linearize(ctxt, addr, size, false, true, &linear);
+		if (rc != X86EMUL_CONTINUE)
+			return rc;
 		rc = ops->fetch(linear, fc->data + cur_size,
 				size, ctxt->vcpu, &ctxt->exception);
 		if (rc != X86EMUL_CONTINUE)
@@ -3127,7 +3138,6 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 	c->fetch.end = c->fetch.start + insn_len;
 	if (insn_len > 0)
 		memcpy(c->fetch.data, insn, insn_len);
-	ctxt->cs_base = seg_base(ctxt, ops, VCPU_SREG_CS);
 
 	switch (mode) {
 	case X86EMUL_MODE_REAL: