Re: [PATCH v4 2/2] ACPICA: Preserve memory opregion mappings

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Jul 16, 2020 at 9:22 PM Verma, Vishal L
<vishal.l.verma@intel.com> wrote:
>
> On Mon, 2020-06-29 at 18:33 +0200, Rafael J. Wysocki wrote:
> > From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> >
> > The ACPICA's strategy with respect to the handling of memory mappings
> > associated with memory operation regions is to avoid mapping the
> > entire region at once which may be problematic at least in principle
> > (for example, it may lead to conflicts with overlapping mappings
> > having different attributes created by drivers).  It may also be
> > wasteful, because memory opregions on some systems take up vast
> > chunks of address space while the fields in those regions actually
> > accessed by AML are sparsely distributed.
> >
> > For this reason, a one-page "window" is mapped for a given opregion
> > on the first memory access through it and if that "window" does not
> > cover an address range accessed through that opregion subsequently,
> > it is unmapped and a new "window" is mapped to replace it.  Next,
> > if the new "window" is not sufficient to acess memory through the
> > opregion in question in the future, it will be replaced with yet
> > another "window" and so on.  That may lead to a suboptimal sequence
> > of memory mapping and unmapping operations, for example if two fields
> > in one opregion separated from each other by a sufficiently wide
> > chunk of unused address space are accessed in an alternating pattern.
> >
> > The situation may still be suboptimal if the deferred unmapping
> > introduced previously is supported by the OS layer.  For instance,
> > the alternating memory access pattern mentioned above may produce
> > a relatively long list of mappings to release with substantial
> > duplication among the entries in it, which could be avoided if
> > acpi_ex_system_memory_space_handler() did not release the mapping
> > used by it previously as soon as the current access was not covered
> > by it.
> >
> > In order to improve that, modify acpi_ex_system_memory_space_handler()
> > to preserve all of the memory mappings created by it until the memory
> > regions associated with them go away.
> >
> > Accordingly, update acpi_ev_system_memory_region_setup() to unmap all
> > memory associated with memory opregions that go away.
> >
> > Reported-by: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/acpi/acpica/evrgnini.c | 14 ++++----
> >  drivers/acpi/acpica/exregion.c | 65 ++++++++++++++++++++++++----------
> >  include/acpi/actypes.h         | 12 +++++--
> >  3 files changed, 64 insertions(+), 27 deletions(-)
> >
>
> Hi Rafael,
>
> Picking up from Dan while he's out - I had these patches tested by the
> original reporter, and they work fine. I see you had them staged in the
> acpica-osl branch. Is that slated to go in during the 5.9 merge window?

Yes, it is.

> You can add:
> Tested-by: Xiang Li <xiang.z.li@intel.com>

Thank you!