linux-kernel - [RFT][PATCH v3 0/4] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

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Message-ID: <2788992.3K7huLjdjL@kreacher>
Date:   Fri, 26 Jun 2020 19:28:27 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Dan Williams <dan.j.williams@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>
Cc:     rafael.j.wysocki@...el.com, Len Brown <lenb@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Ira Weiny <ira.weiny@...el.com>,
        James Morse <james.morse@....com>,
        Myron Stowe <myron.stowe@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-nvdimm@...ts.01.org, Bob Moore <robert.moore@...el.com>
Subject: [RFT][PATCH v3 0/4] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

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