[RFT][PATCH 0/3] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

[Rafael J. Wysocki]

Hi All,

This series is to address the problem with RCU synchronization occurring,
possibly relatively often, inside of acpi_ex_system_memory_space_handler(),
when the namespace and interpreter mutexes are held.

The basic idea is to avoid the actual unmapping of memory in
acpi_ex_system_memory_space_handler() by making it take the advantage of the
reference counting of memory mappings utilized by the OSL layer in Linux.

The basic assumption in patch [1/3] is that if the special
ACPI_OS_MAP_MEMORY_FAST_PATH() macro is present, it can be used to increment
the reference counter of a known-existing memory mapping in the OS layer
which then is dropped by the subsequent acpi_os_unmap_memory() without
unmapping the address range at hand.  That can be utilized by
acpi_ex_system_memory_space_handler() to prevent the reference counters of
all mappings used by it from dropping down to 0 (which also prevents the
address ranges associated with them from being unmapped) so that they can
be unmapped later (specifically, at the operation region deactivation time).

Patch [2/3] defers the unmapping even further, until the namespace and
interpreter mutexes are released, to avoid invoking the RCU synchronization
under theses mutexes.

Finally, patch [3/3] changes the OS layer in Linux to provide the
ACPI_OS_MAP_MEMORY_FAST_PATH() macro.

Note that if this macro is not defined, the code works the way it used to.

The series is available from the git branch at

 git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git \
 acpica-osl

for easier testing.

Cheers,
Rafael