Messages in this thread | | | Subject | Re: [PATCH] arm64: support ACPI tables outside of kernel RAM | From | Mark Salter <> | Date | Mon, 18 May 2015 09:58:45 -0400 |
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On Mon, 2015-05-18 at 12:11 +0100, Catalin Marinas wrote: > On Thu, May 14, 2015 at 10:22:53AM -0400, Mark Salter wrote: > > There is no guarantee that ACPI tables will be located in RAM linearly > > mapped by the kernel. This could be because UEFI placed them below the > > kernel image or because mem= places them beyond the reach of the linear > > kernel mapping. Even though these tables are outside the linear mapped > > RAM, they still need to be accessed as normal memory in order to support > > unaligned accesses from ACPI code. In this case, the page_is_ram() test > > in acpi_os_ioremap() is not sufficient. > > And can we not simply add the rest of the RAM to the resource list as > "System RAM" without being part of memblock?
If it is in "System RAM", then it needs a valid pfn and struct page. Parts of the kernel expect that (page_is_ram(), memory hotplug, etc).
> > > Additionally, if the table spans multiple pages, it may fall partially > > within the linear map and partially without. If the table overlaps the > > end of the linear map, the test for whether or not to use the existing > > mapping in ioremap_cache() could lead to a panic when ACPI code tries > > to access the part beyond the end of the linear map. This patch > > attempts to address these problems. > > That's a problem with ioremap_cache() that should be fixed independently.
I can submit that separately if you prefer.
> > Ideally, I'd like to see the ACPI code use different APIs to distinguish > between table access in RAM and device access, so that we don't have to > guess whether the page is RAM or not. >
I don't think the ACPI code has enough info to make that decision, but I'm not sure honestly.
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