[Xen-devel] Re: [PATCH 2/4] x86,xen: introduce x86_init.mapping.pagetable_reserve

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 18 Apr 2011, H. Peter Anvin wrote:
> On 04/18/2011 07:09 AM, Stefano Stabellini wrote:
> > 
> > Sorry, I don't mean to be pushy, it is just that I'll be AFK for 12 days
> > starting from next Friday and I think that this issue should really be
> > fixed in time for the 2.6.39 release, otherwise no 2.6.39 kernels will
> > be able to boot on any xen system.
> 
> YOU STILL HAVEN'T PROPOSED ANY SEMANTICS.
> 
> The semantics of a hook is a description of what the preconditions are,
> what the postconditions are, and what exactly they are allowed or not
> allowed to do.
> 
> This is a real pain to do, *exactly because hooks are a real pain*.
> Most hooks that have been put in has been "oh, just do something at
> point X in the code", which is a case of definition by implementation,
> which is exactly how we ended up with the current mess.
> 


x86_init.mapping.pagetable_setup_start(start, max_end)

    Notifies the subarch that the kernel early startup intends to
    use pages as page table pages.
    These pages will have physical addresses in the range
    start..max_end.

    Can be called multiple times to setup kernel page table pages,
    always in a pair with x86_init.mapping.pagetable_setup_done.
    It must be called before x86_init.paging.pagetable_setup_start().

    Preconditions: no kernel code after the 32-bit kernel entry point
    has hooked any new page table pages into the active page table
    except between a pair of
    x86_init.mapping.pagetable_setup_start and
    x86_init.mapping.pagetable_setup_done.

    Postcondition: pages in the range start..max_end may be used as
    page table pages and hooked into active page tables.
    Pages in this range may NOT be used for any other purpose.


x86_init.mapping.pagetable_setup_done(real_end)

    Notifies the subarch that the initial memory mapping is complete,
    and of the actual range of pages used.

    Preconditions:

    x86_init.mapping.pagetable_setup_start was previously called; the
    arguments to the calls must satisfy start <= real_end <= max_end

    The pages in the range start..real_end have been hooked into the
    active page table.
    The pages in the range real_end..max_end are not currently in use.

    Postconditions:

    Pages in the range real_end..max_end may be used as normal
    memory.

    Pages in the range start..real_end might be hooked into the active
    page table and cannot be used for other purposes.

    New page table pages must be allocated using
    pv_mmu_ops.alloc_pte/pmd/pud.

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