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    SubjectRe: i486 emu in mainline?
    Willy Tarreau <> wrote:
    > On Sun, May 23, 2004 at 09:13:20AM +0200, Arjan van de Ven wrote:
    > > on first look it seems to be missing a bunch of get_user() calls and
    > > does direct access instead....
    > It was intentional for speed purpose. The areas are checked once with
    > verify_area() when we need to access memory, then data is copied directly
    > from/to memory. I don't think there's any risk, but I can be wrong.

    verify_area() simply checks that the address is a legal one for a userspace
    access (it's not a chunk of kernel memory). But the kernel can still take
    a pagefault when accessing the address, so you need to use the uaccess
    functions which will handle the fault appropriately.

    That's put_user(), get_user(), copy_*_user(), etc. Those functions
    internally perform verify_area(), so if you've already done a verify_area()
    you can use __put_user(), __get_user(), etc which skip the verify_area()
    but which still know how to deal with user address faults.

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      Last update: 2005-03-22 14:03    [W:0.020 / U:0.224 seconds]
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