Some ACPI IO accessing need to be done in atomic context. For example,
APEI ERST operations may be used for permanent storage in hardware
error handler. That is, it may be called in atomic contexts such as
IRQ or NMI, etc. And, ERST/EINJ implement their operations via IO
memory/port accessing. But the IO memory accessing method provided by
ACPI (acpi_read/acpi_write) maps the IO memory during it is accessed,
so it can not be used in atomic context. To solve the issue, the IO
memory should be pre-mapped during EINJ/ERST initializing. A linked
list is used to record which memory area has been mapped, when memory
is accessed in hardware error handler, search the linked list for the
mapped virtual address from the given physical address.

Signed-off-by: Huang Ying
Signed-off-by: Andi Kleen
Signed-off-by: Len Brown