Messages in this thread | | | Date | Mon, 21 Jan 2008 13:38:22 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] x86: Construct 32 bit boot time page tables in native format. |
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Ian Campbell wrote: > On Sun, 2008-01-20 at 20:30 +0200, Mika Penttilä wrote: >>> >> You have dropped the requirement to map all of low memory (the boot >> allocator is used for instance to construct physical mem mapping). >> Either you should fix your INIT_MAP_BEYOND_END or make a big comment >> telling us why it isn't necessary anymore to map low mem. > > I think you are right. The patch ensures that all the initial page > tables themselves have mappings but won't map the additional pages > needed for mapping the rest of lowmem. > > However, I think it is no longer necessary to map a whole new 4G worth > of page table pages because the code in kernel_physical_mapping_init now > extends the initial mappings rather than replacing them (see changes to > native_pagetable_setup_start). So now we only need to map 4G worth of > page tables including the initial page tables. That means we only need > to map a fixed set of extra pages rather than the sliding limit > currently used in the patch. >
We still need to be able to construct those page tables, which is what that stuff is about...
> I'm not convinced by the additional 16MB for CONFIG_DEBUG_PAGEALLOC -- > we map enough pages for page tables for 4G of lowmem -- adding space for > an extra 16M seems pointless.
If so, adjusting the limit should be a separate patch.
Either way, I'm increasingly thinking that setting up the initial page tables via an assembly loop instead of worrying about the C accessors is actually cleaner (I prototyped it yesterday, although I still need the rest of the machinery.)
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