Re: [PATCH]Fix broken VMI in 2.6.27-rc..

[Jeremy Fitzhardinge <jeremy@goop.org>]

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