Messages in this thread | | | Subject | Re: [PATCH] arm64: support ACPI tables outside of kernel RAM | From | Mark Salter <> | Date | Fri, 22 May 2015 09:13:24 -0400 |
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On Fri, 2015-05-22 at 13:53 +0100, Catalin Marinas wrote: > On Fri, May 22, 2015 at 08:46:02AM -0400, Mark Salter wrote: > > On Fri, 2015-05-22 at 11:34 +0100, Catalin Marinas wrote: > > > OK, so my preferred options, in this order: > > > > > > 1. Change the core ACPI kernel code to distinguish between mapping I/O > > > or RAM (could be as simple as acpi_map not using acpi_os_ioremap but > > > another API). I guess the code knows when it plans to map tables or > > > I/O registers > > > > > > 2. If the above is not possible, add the extra checks as per Mark's > > > patch but I would rather call this resource "UEFI RAM" than "ACPI", > > > it's not really ACPI specific. > > > > Actually, it is ACPI specific. The patch only registers resources for > > EfiACPIReclaimMemory and EfiACPIMemoryNVS regions which are also > > marked as cacheable. On x86 these show up in /proc/iomem as > > "ACPI Tables" and "ACPI Non-volatile Storage". I used "ACPI RAM" to > > avoid having to search for two strings. > > My point is more about UEFI describing the entire RAM while the kernel > command line restricts it via "mem=". In this case, the "System RAM" > resources is reduced as well but it does not necessarily mean that the > rest of the RAM is only used by ACPI. >
Ah okay. But I'm not sure we want the kernel to access other areas cut off by mem=. The case I'm dealing with which led to this patch was a kdump dump-collection kernel. For that kernel, we really don't want it accessing any general purpose memory outside of its system ram. For the dump collection, it already uses ioremap_cache to get to crash-kernel memory. The reason for the iomem resources added for the UEFI ACPI regions was so the dump-collection kernel could boot using ACPI.
That being said, I could rework the patch to add all "UEFI RAM" and that would let us just check that one string for acpi_os_ioremap() purposes rather than checking "System RAM" and "ACPI RAM".
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