On Fri, May 30, 2014 at 12:25 PM, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > On Fri, 30 May 2014, Rob Herring wrote: > >> There's work in flight to support early_ioremap, early console, and RO >> text patching which all use the fixmap region. >> >> There's a couple of options to solve this: >> >> - Only support up to 16 cpus. It could be anywhere between 17-31, but >> that seems somewhat unlikely. Are we really ever going to see 32-bit >> 32 core systems? > > I wouldn't rule that out. I've seen 16-core ARM chips in 2008 (although > they didn't go into production). Silly limitations like that always > come back to bite you. And we have better alternatives. > >> - Reduce KM_TYPE_NR from 16 to 15. Based on the comment for it, we >> probably don't want to do that. Is increasing it to the default of 20 >> worthwhile? Some of the options here would allow doing that. >> - Add 0xffe00000-0xfff00000 to the fixmap region. This would make >> fixmap span 2 PMDs with the top PMD having a mixture of uses like we >> had before. > > That would be my preferred approach. Note here it could be > 0xffe00000-0xfffe0000 to include the whole of the previous fixmap area > curently unused. > >> - push the PCI i/o space down to 0xfec00000 and make fixmap 4MB. This >> is a cleaner solution as the 2 PMDs are only used for fixmap. This may >> require some static mapping adjustments on some platforms. > > No need. With the latest changes, the fixmap area is between 0xffc00000 > and 0xffe00000 (there is apparently a mistake in > Documentation/arm/memory.txt). So currently 0xff000000-0xffc00000 is > free, which makes the fixmap area far away from the PCI i/o area with > plenti of space in between.
So, it seems there is something wrong with this patch series. I had to revert "ARM: 8031/2: change fixmap mapping region to support 32 CPUs" to make other fixmap changes work correctly. I think this is due to the non-highmem config case moving the fixmap to a location where there is to page table entry... -Kees > >> - Same as previous option, but convert the PCI i/o space to fixmap >> entries. We don't really need all 2MB for PCI. > > See above. > >> Also, there is an error in the documentation below: >> >> > >> > Signed-off-by: Liu Hua <sdu....@huawei.com> >> > --- >> > Documentation/arm/memory.txt | 2 +- > > Yep, good that you spotted it as well. I failed to catch it during my > review so I'll send a patch. > > > Nicolas > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-ker...@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
