On 5 February 2015 at 12:07, Catalin Marinas catalin.marinas@arm.com 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@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.
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.