x86: Fix 'reservetop=' functionality

When specifying the 'reservetop=0xbadc0de' kernel parameter,
the kernel will stop booting due to a early_ioremap bug that
relates to commit 8827247ff.

The root cause of boot failure problem is the value of
'slot_virt[i]' was initialized in setup_arch->early_ioremap_init().
But later in setup_arch, the function 'parse_early_param' will
modify 'FIXADDR_TOP' when 'reservetop=0xbadc0de' being specified.

The simplest fix might be use __fix_to_virt(idx0) to get updated
value of 'FIXADDR_TOP' in '__early_ioremap' instead of reference
old value from slot_virt[slot] directly.

Changelog since v0:

-v1: When reservetop being handled then FIXADDR_TOP get
     adjusted, Hence check prev_map then re-initialize slot_virt and
     PMD based on new FIXADDR_TOP.

-v2: place fixup_early_ioremap hence call early_ioremap_init in
     reserve_top_address  to re-initialize slot_virt and
     corresponding PMD when parse_reservertop

-v3: move fixup_early_ioremap out of reserve_top_address to make
     sure other clients of reserve_top_address like xen/lguest won't
     broken

Signed-off-by: Liang Li <liang.li@windriver.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Wang Chen <wangchen@cn.fujitsu.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <1272621711-8683-1-git-send-email-liang.li@windriver.com>
[ fixed three small cleanliness details in fixup_early_ioremap() ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/io.h

@@ -347,6 +347,7 @@ extern void __iomem *early_ioremap(resource_size_t phys_addr,
 extern void __iomem *early_memremap(resource_size_t phys_addr,
 				    unsigned long size);
 extern void early_iounmap(void __iomem *addr, unsigned long size);
+extern void fixup_early_ioremap(void);
 
 #define IO_SPACE_LIMIT 0xffff
 

arch/x86/mm/ioremap.c

@@ -448,6 +448,20 @@ static inline void __init early_clear_fixmap(enum fixed_addresses idx)
 static void __iomem *prev_map[FIX_BTMAPS_SLOTS] __initdata;
 static unsigned long prev_size[FIX_BTMAPS_SLOTS] __initdata;
 
+void __init fixup_early_ioremap(void)
+{
+	int i;
+
+	for (i = 0; i < FIX_BTMAPS_SLOTS; i++) {
+		if (prev_map[i]) {
+			WARN_ON(1);
+			break;
+		}
+	}
+
+	early_ioremap_init();
+}
+
 static int __init check_early_ioremap_leak(void)
 {
 	int count = 0;

arch/x86/mm/pgtable_32.c

@@ -128,6 +128,7 @@ static int __init parse_reservetop(char *arg)
 
 	address = memparse(arg, &arg);
 	reserve_top_address(address);
+	fixup_early_ioremap();
 	return 0;
 }
 early_param("reservetop", parse_reservetop);