On Wed, Feb 03, 2010 at 02:22:50PM -0800, Guenter Roeck wrote: > since it came up during the review of the patch for virtual memory detection > on 64 bit mips kernels, I looked further into making vmalloc_end > a variable and TASK_SIZE dependent on the virtual memory size. > > That turned out to be relatively straightforward, and I have a working patch. > > The one question I still have is about FIXADDR_START. It is currently > set to one of 0xff000000, 0xfffe0000, or (0xff000000 - 0x20000), > depending on the target CPU. > > Quoting from one of the comments during the review, > " ... ensure the value of vmalloc_end is <= FIXADDR_START". > > Obviously that is currently not the case. Is that a concern, or is it good as it is ? Now with allocations potencially happening top-down this is potencially a serious problem. Details would depend on details of platform, processor and kernel configuration. I said vmalloc_end is <= FIXADDR_START" but more accurately we simply need to avoid a conflict between the different virtual address space users. Some CPUs have fixed mappings in their hardware in the KSEG2/KSEG3 range; those mappings can't be overriden by a TLB mapping. To deal with that sort of architectural candy I think a call into the address space allocator for kernel virtual memory is probably nicest thing but something simplier than that would probable have to do for 2.6.34. Ralf
