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

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Date:   Sat, 13 Jun 2020 21:19:28 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        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: Re: [RFT][PATCH 0/3] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

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!