ACPI, APEI Fix the return value(==NULL) of acpi_pre_map().

acpi_pre_map() is used for remapping the physical address of I/O, so it should be return NULL or remapped virtual address. The problem is that when (paddr - pg_off) equals 0, no matter whether I/O remapping is successful or not, the function returns NULL.

In acpi_pre_map(), after the physical address is remapped sucessfully, it will check whether the physical address has been added into acpi_iomaps list again.
- If the physical address has beed added into acpi_iomaps, the virtual address will be saved in vaddr.
- Otherwise, NULL be saved in vaddr.

So if the physical address is the first time to be remapped, vaddr will be NULL always.

In many cases, (paddr - pg_off) may not equal 0. So the function could work well. In our machine, (paddr - pg_off) equals 0, so the return value of acpi_pre_map() is NULL.

This patch fixed it and I confirmed it on x86_64 next-tree.

---
 drivers/acpi/atomicio.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

index 8f8bd73..1bc2614 100644
@@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 
 	spin_lock_irqsave(&acpi_iomaps_lock, flags);
 	vaddr = __acpi_try_ioremap(paddr, size);
-	if (vaddr) {
+	if (unlikely(vaddr)) {
 		spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 		iounmap(map->vaddr);
 		kfree(map);

@@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 	list_add_tail_rcu(&map->list, &acpi_iomaps);
 	spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 
-	return vaddr + (paddr - pg_off);
+	return map->vaddr + (paddr - pg_off);
 err_unmap:
 	iounmap(vaddr);
 	return NULL;

1.7.1.1

Best Regards,
Huang Ying