On Thu, Feb 05, 2015 at 10:16:03PM +0000, Ard Biesheuvel wrote: > On 5 February 2015 at 17:48, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Thu, Feb 05, 2015 at 04:42:19PM +0000, Al Stone wrote: > >> On 02/05/2015 06:54 AM, Mark Salter wrote: > >> > On Thu, 2015-02-05 at 10:41 +0000, Catalin Marinas 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. > >> > > >> > The problem with kmap() is that it only maps a single page. I've seen > >> > tables over 4k which is why I patched acpi_map() not to use kmap() on > >> > arm64. > >> > >> Right. Mark replied to this before I could; using kmap() enforced a 4k > >> (one page) limit that we kept breaking with some ACPI tables being larger > >> than that (DSDTs and SSDTs, fwiw). This would lead to some very odd behaviors > >> when most but not all of a device definition was within the page; using the > >> table checksums was one way of detecting the issues. > > > > OK. So I think Mark's original patch was ok, assuming that the System > > Memory cases mentioned by Graeme are detected with page_is_ram(). > > page_is_ram() returns whether a pfn is covered by the linear mapping, > so memory before the kernel or after a mem= limit will be > misidentified. OK. So in conclusion acpi_os_ioremap() may need to create a cacheable mapping even when !page_is_ram() but it has no way of knowing that unless we change the core ACPI code to differentiate between ioremap_cache and ioremap_nocache. Did I get it right? -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
