Re: Page table and memory management

[Richard <judicator3@gmail.com>]

Hi,

I think the flow graph in the previous email was too big and might not
display properly:

               do_mmu_update
                     |
                     |
    /---------------------------------\
    |                                 |
    |                                 |
    \/                                \/
 mod_l2_entry              do_extended_command
    |                                 |
    |                                 |
    \/                                |
get_page_from_l2e                     |
    |                                 |
    |                                 |
    \---------------------------------/
                     |
                     |
                     \/
          get_page_and_type_from_pagenr
                     |
                     |
                     \/
               get_page_type

Richard


On Thu, 3 Mar 2005 17:00:17 -0500, Richard <judicator3@gmail.com> wrote:
> Hi Keir,
> 
> I am still having trouble to edit the page table entries with the
> mmu_update hypercall.
> I am actually updating the mini-os. The mem management in mini-os is
> pretty outdated. For example, it assumes that the initial page tables
> are placed at the top of available memory and hence does not count
> properly the total amount of pages that have been allocated to the
> domain. I am extending the initial PGD and PT given to mini-os at boot
> time to map the available memory that I can use.
> 
> I tried to first pin a level 1 page frame before inserting it as an
> entry in the level 2 PGD.
> Whether I pin a level1 page frame first or I start using it directly
> as a page table, it does not matter the mmu_update hypercall still
> fails.
> 
> I traced through the XEN code, in the file arch/x86/memory.c. Whether
> excuting a MMU_NORMAL_PT_UPDATE or a MMU_EXTENDED_COMMAND type of
> command, the function do_mmu_update() eventually calls the helper
> function get_page_and_type_from_pagenr() which in turns call the
> function get_page_type(). Below I drew a call graph.
> 
>                                                  do_mmu_update
>                                                             |
>                                                             |
> 
> /------------------------------------------------------------------------------\
>                        |
>                                |
>                        \/
>                                \/
>                mod_l2_entry
>    do_extended_command
>                        |
>                                |
>                        \/
>                                |
>             get_page_from_l2e
>                     |
>                        |
>                                |
>                        |
>                                |
> 
> \------------------------------------------------------------------------------/
>                                                               |
>                                                               \/
>                                         get_page_and_type_from_pagenr
>                                                               |
>                                                               \/
>                                                      get_page_type
> 
> The get_page_type() checks the upperbits of the 'typeinfo' field of
> the page frame to make sure it is of type 'PGT_l1_page_table'.
> get_page_type() also does another check to verify that the 'typeinfo'
> field also contains the 10 upper bits of the virtual address that this
> page frame is suppose to eventually map to.
> 
> > Xen will automatically infer the type when you attach an L1 to an
> > existing L2. Xen will infer the L2 type when the L2 gets used as
> > current pagetable base.
> So I do not see where XEN is automatically inferring the L1 type when
> I am inserting for the 1st time the L1 page frame into the L2. In
> order to use a page frame as an L1 page table, I have to find a way to
> tell XEN to update the corresponding typeinfo field in order to pass
> the verification in get_page_type().
> 
> Thanks
> Richard
>


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