[PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64

[Graeme Gregory]

On Thu, Feb 05, 2015 at 10:59:45AM +0000, Catalin Marinas wrote:
> On Thu, Feb 05, 2015 at 10:47:23AM +0000, Ard Biesheuvel wrote:
> > On 5 February 2015 at 10:41, Catalin Marinas <catalin.marinas at arm.com> wrote:
> > > On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote:
> > >> On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote:
> > >> > On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote:
> > >> > > acpi_os_remap() is used to map ACPI tables. These tables may be in ram
> > >> > > which are already included in the kernel's linear RAM mapping. So we
> > >> > > need ioremap_cache to avoid two mappings to the same physical page
> > >> > > having different caching attributes.
> > >> >
> > >> > What's the call path to acpi_os_ioremap() on such tables already in the
> > >> > linear mapping? I can see an acpi_map() function which already takes
> > >> > care of the RAM mapping case but there are other cases where
> > >> > acpi_os_ioremap() is called directly. For example,
> > >> > acpi_os_read_memory(), can it be called on both RAM and I/O?
> > >>
> > >> acpi_map() is the one I've seen.
> > >
> > > By default, if should_use_kmap() is not patched for arm64, it translates
> > > to page_is_ram(); acpi_map() would simply use a kmap() which returns the
> > > current kernel linear mapping on arm64.
> > >
> > >> I'm not sure about others.
> > >
> > > Question for the ARM ACPI guys: what happens if you implement
> > > acpi_os_ioremap() on arm64 as just ioremap()? Do you get any WARN_ON()
> > > (__ioremap_caller() checks whether the memory is RAM)?
> > 
> > Regardless of whether you hit any WARN_ON()s now,
> 
> Actually following the WARN_ON(), ioremap() returns NULL, so it may not
> go entirely unnoticed.
> 
> > we still need to distinguish between MMIO ranges with device
> > semantics, and ACPI or other tables whose data may not be naturally
> > aligned all the time, and hence requiring memory semantics.
> > acpi_os_ioremap() may be used for both, afaik
> 
> Is acpi_os_ioremap() called directly (outside acpi_map()) to map RAM
> that already part of the kernel linear memory? If yes, then I agree that
> we need to do such check.
> 
> Another question, can we distinguish, in the ACPI core code, whether the
> mapping is for an ACPI table in RAM or some I/O space?
> 

Yes I think we do,

acpi_os_map_memory() is called to map tables

acpi_os_map_iomem() is called to map device IO

currently both end up in acpi_map but I guess they do not have to or
we can add extra arguments as its an internal API.

But I have not checked that no user sneaks in direct calls.

Graeme