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[RFT,v3,0/4] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

Message ID 2788992.3K7huLjdjL@kreacher
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Series ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter | expand

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Rafael J. Wysocki June 26, 2020, 5:28 p.m. UTC 
Hi All,

On Monday, June 22, 2020 3:50:42 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.
> 
> Like I said before, I had decided to change the approach used in the previous
> iteration of this series and to allow the unmap operations carried out by 
> acpi_ex_system_memory_space_handler() to be deferred in the first place,
> which is done in patches [1-2/4].

In the meantime I realized that calling syncrhonize_rcu_expedited() under the
"tables" mutex within ACPICA is not quite a good idea too and that there is no
reason for any users of acpi_os_unmap_memory() in the tree to use the "sync"
variant of unmapping.

So, unless I'm missing something, acpi_os_unmap_memory() can be changed to
always defer the final unmapping and the only ACPICA change needed to support
that is the addition of the acpi_os_release_unused_mappings() call to get rid
of the unused mappings when leaving the interpreter (module the extra call in
the debug code for consistency).

So patches [1-2/4] have been changed accordingly.

> However, it turns out that the "fast-path" mapping is still useful on top of
> the above to reduce the number of ioremap-iounmap cycles for the same address
> range and so it is introduced by patches [3-4/4].

Patches [3-4/4] still do what they did, but they have been simplified a bit
after rebasing on top of the new [1-2/4].

The below information is still valid, but it applies to the v3, of course.

> For details, please refer to the patch changelogs.
> 
> 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.

Also the series have been tested locally.

Thanks,
Rafael