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

[Ard Biesheuvel]

On 5 February 2015 at 12:07, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> On Thu, Feb 05, 2015 at 11:14:43AM +0000, Graeme Gregory wrote:
>> 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@xxxxxxx> 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.
>
> Ending up in acpi_map() is ok as this function checks whether it should
> use kmap() or acpi_os_ioremap().
>

This still only addresses the mismatched attributes part: regions that
require memory semantics may still end up being mapped as device
memory if they are not covered by the linear mapping, which could
happen if the region resides below the kernel in memory, or if we
passed a mem= parameter and it sits at the very top.

>> But I have not checked that no user sneaks in direct calls.
>
> Grep'ing for acpi_os_ioremap():
>
> suspend_nvs_save() - we don't care about this yet for arm64 as the
> function is only compiled in if CONFIG_ACPI_SLEEP
>
> acpi_os_read_memory() and acpi_os_write_memory() - do you know what kind
> of memory are these used on?
>
> couple of intel drm files that are not used on arm.
>

-- 
Ard.
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