ACPI/APEI: fix ERST MOVE_DATA instruction implementation

The src_base and dst_base fields in apei_exec_context are physical
address, so they should be ioremaped before being used in ERST
MOVE_DATA instruction.

Reported-by: Javier Martinez Canillas <martinez.javier@xxxxxxxxx>
Reported-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>

Replace use of ioremap() by __acpi_map_table()/set_fixmap(). Fix error
handling.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Note that I have no way to test this code other than by having it go
through the tester, since I have no hardware available to reproduce
the regression found there (in other words, this is just a blind
attempt at addressing the problem uncovered by 26060:4fc87c2f31a0).

--- a/xen/drivers/acpi/apei/erst.c
+++ b/xen/drivers/acpi/apei/erst.c
@@ -247,15 +247,64 @@ static int erst_exec_move_data(struct ap
 {
 	int rc;
 	u64 offset;
+#ifdef CONFIG_X86
+	enum fixed_addresses idx;
+#endif
+	void *src, *dst;
+
+	/* ioremap does not work in interrupt context */
+	if (in_irq()) {
+		printk(KERN_WARNING
+		       "MOVE_DATA cannot be used in interrupt context\n");
+		return -EBUSY;
+	}
 
 	rc = __apei_exec_read_register(entry, &offset);
 	if (rc)
 		return rc;
-	memmove((void *)(unsigned long)(ctx->dst_base + offset),
-		(void *)(unsigned long)(ctx->src_base + offset),
-		ctx->var2);
 
-	return 0;
+#ifdef CONFIG_X86
+	switch (ctx->var2) {
+	case 0:
+		return 0;
+	case 1 ... PAGE_SIZE:
+		break;
+	default:
+		printk(KERN_WARNING
+		       "MOVE_DATA cannot be used for %#"PRIx64" bytes of data\n",
+		       ctx->var2);
+		return -EOPNOTSUPP;
+	}
+
+	src = __acpi_map_table(ctx->src_base + offset, ctx->var2);
+#else
+	src = ioremap(ctx->src_base + offset, ctx->var2);
+#endif
+	if (!src)
+		return -ENOMEM;
+
+#ifdef CONFIG_X86
+	BUILD_BUG_ON(FIX_ACPI_PAGES < 4);
+	idx = virt_to_fix((unsigned long)src + 2 * PAGE_SIZE);
+	offset += ctx->dst_base;
+	dst = (void *)fix_to_virt(idx) + (offset & ~PAGE_MASK);
+	set_fixmap(idx, offset);
+	if (PFN_DOWN(offset) != PFN_DOWN(offset + ctx->var2 - 1)) {
+		idx = virt_to_fix((unsigned long)dst + PAGE_SIZE);
+		set_fixmap(idx, offset + PAGE_SIZE);
+	}
+#else
+	dst = ioremap(ctx->dst_base + offset, ctx->var2);
+#endif
+	if (dst) {
+		memmove(dst, src, ctx->var2);
+		iounmap(dst);
+	} else
+		rc = -ENOMEM;
+
+	iounmap(src);
+
+	return rc;
 }
 
 static struct apei_exec_ins_type erst_ins_type[] = {