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SubjectRe: [RFT][PATCH 0/3] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter
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On Wednesday, June 10, 2020 2:17:04 PM CEST Rafael J. Wysocki wrote:
> 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.

Please disregard this patch series, it will be replaced by a new one which
already is there in the acpica-osl branch above.

Thanks!



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