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    SubjectRe: linux page table
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    On Sun, Sep 2, 2012 at 1:10 AM, Jiri Kosina <jkosina@suse.cz> wrote:
    > On Sat, 1 Sep 2012, Xin Tong wrote:
    >
    >> When a process is created in Linux, corresponding page table is
    >> implemented. In the current x86 linux, the page table is a multi-level
    >> page table and CR3 points to the first level of the page table. I
    >> have 2 questions.
    >>
    >> 1. is the value in CR3 virtual address or physical address ?
    >
    > Physical, otherwise you will have chicken-egg problem.
    >
    >> 2. can the address of the first level of the page table during a
    >> process's lifetime change ?
    >
    > In theory it would be possible to implement. But I don't see a scenario
    > when it might be useful.
    >
    >> 3. can two different processes have their CR3 being the same value
    >> even though they have different first level page tables ?
    >
    > Yes, if they are created by clone(CLONE_VM). In such case they share the
    > same mm_struct, and therefore mm_struct->pgd (which is exactly what is
    > loaded into cr3 in switch_mm()) is the same.
    >

    Is this the COW mechanism in linux. what if the cloned process need to
    have set of its own pages later. do the CR3s for the 2 processes
    become different at that point ?

    > LKML is however very inappropriate list for such questions. Please ask on
    > kernelnewbies list next time.
    >

    Thank you for letting me know. Will do next time.
    > --
    > Jiri Kosina
    > SUSE Labs
    >


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