Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings

Jeremy Fitzhardinge
2007-04-23T18:07:28Z

Eric W. Biederman wrote:
> Consider a memory hole of size 8M immediately after our bootmem bitmap.
> head.S which knows nothing of holes will map the pages of the hole
> into the initial page tables assuming that is where the page tables
> will live.
>

Sure, but considering we're only talking about mapping an additional *2*
pages, the chances are that it will affect a kernel as much as the early
head.S mapping. It's well within the variability of fairly similar
kernel configs.

> As for how to fix this, we need to call boot_ioremap or better
> bt_ioremap on the address returned from alloc_bootmem_pages_low to
> force the allocated page into the page table. After we have setup
> the page table page we can call unmap the page to free up the scarce
> early mapping resource.
>

Would that be necessary? Is there any need to remap it? Couldn't you
just do the straightforward phys->virt mapping and use the page where it
lies?

J