Messages in this thread | | | Subject | Re: [PATCH]Fix broken VMI in 2.6.27-rc.. | From | Zachary Amsden <> | Date | Thu, 07 Aug 2008 14:55:54 -0700 |
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On Thu, 2008-08-07 at 14:52 -0700, H. Peter Anvin wrote: > Zachary Amsden wrote: > >>> > >> Okay, you lost me about halfway through that... could you perhaps > >> describe the problem from the beginning, exactly what you're trying to do? > > > > A kernel compiled with VMI enabled may run on a non-VMI platform. If > > that is the case, the fixmap should not be relocated. If however, a VMI > > ROM is found, we need to hijack up to 64-MB of linear address space from > > the top of memory down. This means moving the fixmap down by the same > > amount. > > > > I take it there are no alternatives other than putting this at the end > of memory?
Nope, it must be in an area allowing for segmentation protection, while keeping the kernel on zero-based segments; that means only the end of linear address space is sufficient.
> Realistically speaking, any (virtual) machine which does *not* have a > full complement of lowmem (i.e. less than 896 MB in the common case) > will not suffer significatly from losing a few megabytes of address space.
Yes, the reason to make the fixmap moveable is to allow as much address space as possible for big memory (physical) machines.
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