Hi, On 08/09/07 22:46, Joachim Worringen wrote: [cut]
Why does map_len have to be page-aligned? devmap(9E) doesn't mention this (says it has to be <= the mmap() len), and the example there does no alignment, too. Also, I tried and returned ptob(btopr((len)), but it did not fix the problem (and violated the maplen <= len constraint - but ptob(btop((len)) wouldn't make sense, either).
A page is the smallest currency unit for the MMU which polices page mappings - you can't expose less than a page from kernel to userland since once the page is loaded into the TLB after the intial pagefault in userland you won't trap again for as long as it remains loaded - so you have no way to stop userland accessing other bits of the page. Perhaps devmap(9E) does not mention that, but it is alluded to in pages such as ddi_umem_alloc(9F) and devmap_umem_setup(9F). Cheers Gavin
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