Page table queries

[anish singh]

On Sat, Feb 19, 2011 at 2:44 PM, Rajat Sharma <fs.rajat at gmail.com> wrote:

> > So, in the start, the page might have kernel mode address, but in the
> > end it has user mode address. But kernel is still the one that tracks
> > all the page...be it anonymous or non anonymous ones.
>
> Not really. In this particular case of .nopage (page fault handler) of
> vma, we already have a user space virtual address for the faulty page,
> we just need it to map it with a physical page frame (RAM or device
> memory). Just allocate a physical page frame without any address,
> caller for .nopage will take care of properly setting its user space
> virtual address (page->va). So, no association with kernel space
> virtual address is required, e.g. it can be high memory page too
> without any kernel mapping.
>
> so after the setting of user space virtual address the physical memory can
be directly addreseed by just doing a page table translation in user space
and kernel doesn't need to be involved.As it has already created the page
table and returned the corresponding page.Am i right?

> Rajat
>
> On Sat, Feb 19, 2011 at 2:10 PM, Mulyadi Santosa
> <mulyadi.santosa at gmail.com> wrote:
> > Hi :)
> >
> > I'll try to help...
> >
> > On Sat, Feb 19, 2011 at 13:10, anish singh <anish198519851985 at gmail.com>
> wrote:
> >> As i understood whenver a user space program is run it is represented in
> >> kernel using VMA which is managed by struct mm_struct
> >> and whenever the program is trying to read/write to a memory location in
> >> user space it will be directed to physical address using PAGE TABLE
> >> translation done by struct mm_struct(done in kernel space).Am i right?
> >
> > i think not "done" but mm_struct points to PGD that represent's the
> > whole process address space. Using information provided there, MMU
> > does translation.
> >
> >> Suppose a simple driver wants the user to directly access its device
> memory
> >> then we use mmap.This mmap associates a set of user space virtual
> address
> >> with device driver memory and it is done by creating kernel page tables
> for
> >> the user space virtual addresses.Is the page table translation done
> >> everytime whenever user space does read/write to the device memory??
> >
> > if it's recently translated, quite likely it is already cached in TLB
> > (translation look aside buffer)
> >
> >> In .nopage function call we return the page associated with the physical
> >> address which the user wants to associate with user space virtual
> address.Is
> >> the page address returned by the nopage function same as seen by the
> user or
> >> will it be converted to user space virtual address(range between 0-2
> GB)?
> >
> > AFAIK, nopage is one of the functions that handle minor page fault, no?
> >
> > Anyway, memory allocation, usually start by kernel allocates a page.
> > Then it is "handed" to user space memory allocator.
> >
> > So, in the start, the page might have kernel mode address, but in the
> > end it has user mode address. But kernel is still the one that tracks
> > all the page...be it anonymous or non anonymous ones.
> >
> > Does it help? :)
> >
> >
> >
> > --
> > regards,
> >
> > Mulyadi Santosa
> > Freelance Linux trainer and consultant
> >
> > blog: the-hydra.blogspot.com
> > training: mulyaditraining.blogspot.com
> >
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>
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