On Mon, 2007-10-15 at 11:45 +1000, David Gibson wrote: > On Sun, Oct 14, 2007 at 08:01:19PM -0500, Josh Boyer wrote: > > On Mon, 2007-10-15 at 10:54 +1000, David Gibson wrote: > > > On Fri, Oct 12, 2007 at 06:56:24AM -0500, Josh Boyer wrote: > > > > On Fri, 2007-10-12 at 13:30 +1000, David Gibson wrote: > > > > > On Thu, Oct 11, 2007 at 01:42:30PM -0500, Kumar Gala wrote: > > > > > > Move to using PAGE_OFFSET instead of TASK_SIZE or KERNELBASE value > > > > > > on > > > > > > 6xx/40x/44x/fsl-booke to determine if the faulting address is a > > > > > > kernel or > > > > > > user space address. This mimics how the macro is_kernel_addr() > > > > > > works. > > > > > > > > > > Actually it's ambiguous whether TASK_SIZE or PAGE_OFFSET is correct in > > > > > most of these cases (KERNELBASE is certainly wrong, though). > > > > > > > > > > TASK_SIZE is the top of the userspace mapped area, PAGE_OFFSET is the > > > > > bottom of the linear mapping. So, strictly speaking there are 3 paths > > > > > for the miss handlers: < TASK_SIZE => user mapping, >= PAGE_OFFSET => > > > > > kernel mapping, between the two => immediate fault. > > > > > > > > > > We get away with a two way comparison on 32-bit because, a) they have > > > > > the same value and b) none of the pagetables, user or kernel, should > > > > > have any entries in the in between region so we'll end up in > > > > > do_page_fault in the end, anyway. > > > > > > > > Kumar's other patch removes the gap. He changed the default > > > > CONFIG_TASK_SIZE to 0xc0000000. > > > > > > That's (a) and only removes the gap in the default configuration.. > > > > I believe the idea was that as defconfigs get updated for 2.6.24, they > > would pick up the new default. > > Yes, but if someone overrides CONFIG_TASK_SIZE, it should still work, > yes? Or else this should not be a CONFIG option at all. Which it > will, of course, because of (b), but one should still be aware of the > theoretical 3-way branch when touching this code, even if it can be > reduced to 2-way branch in practice.
There's a construct involving the characters "/" and "*" which I believe can solve this problem. cheers -- Michael Ellerman OzLabs, IBM Australia Development Lab wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person
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