On Thu, Jul 16, 2020 at 9:22 PM Verma, Vishal L <vishal.l.verma@xxxxxxxxx> wrote: > > On Mon, 2020-06-29 at 18:33 +0200, Rafael J. Wysocki wrote: > > From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> > > > > 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@xxxxxxxxx> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > --- > > 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@xxxxxxxxx> Thank you!
