Messages in this thread | | | Date | Sun, 2 Sep 2012 08:56:34 -0700 | Subject | Re: linux page table | From | Xin Tong <> |
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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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