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    SubjectRe: [PATCH] New phys_addr() syscall
    >>>>> "Alan" == Alan Cox <> writes:


    >> What issues? If I pin down a set of pages, I can then get their
    >> physical address and tell the card to DMA its heart out. How
    >> exactly is this going to fail?

    Alan> DMA doesnt honour the MMU write protect bits for copy on write,
    Alan> or for page locking. Nor does it set the dirty bit on page table
    Alan> entries.

    I should consider this also applies to PCI writes, doesn't it?
    I was thinking of allowing the USB Stack to directly write to user
    pages using PCI. If PCI doesn't also honour the bits we need, could it
    be done by hand as the write is finished?


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