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SubjectRe: [PATCH]Fix broken VMI in 2.6.27-rc..
H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>>>
>>> The Linux kernel was never a paragon of perfection - it was never
>>> meant to be. Just because a bit of cruft went unnoticed into the
>>> kernel doesn't mean we shouldn't fix it.
>>
>> I don't really see what the issue is.
>>
>> Fixmaps are primarily used for things that need to be mapped early
>> before we can allocate address space dynamically. They're
>> predominantly used for boot-time init, and rarely on any
>> performance-critical path. The only vaguely regular use a fixmap
>> gets during runtime is poking at apics, and that's dominated by IO
>> time, and kmap_atomic. Statically, there's only 100 references in
>> the kernel. And it only affects 32-bit.
>>
>> Having fixmaps at link-time fixed addresses would be nice, I suppose,
>> but hardly worth going to vast effort over.
>>
>
> No, but it's hardly vast effort, either.

Thinking about it, the fixmap really has to be as high as possible. If
it were any lower, then it would either truncate the 1:1 mapping, or
shadow some physical memory.

J


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