UEFI Compatibility Issues in Fedora 10

Brian Maly bmaly at redhat.com
Tue Apr 7 15:55:10 UTC 2009

jonathan barkelew wrote:
> The second issue is far more pressing, and much more difficult to 
> solve. The linux kernel will behave
> incorrectly if more than 400k of runtime memory is declared by system 
> firmware. The kernel attempts
> to map all UEFI runtime memory into the kernel fixmap table, and any 
> requests to map more than 400k
> are silently ignored. If this memory is accessed later in the boot 
> process (after transition to virtual
> mode), the kernel will panic. It is my understanding that this 
> mechanism was designed to enable kexec
> functionality, but this mechanism is UEFI non-compliant. If Fedora is 
> ever to be reliably booted on
> UEFI systems, this issue must be addressed.
I had gotten this fixed upstream, committed in the 2.6.29-rc8 kernel. 
efi_ioremap was broken. This should also be in the latest rawhide kernel.
Perhaps you can verify the problem is resolved? If it is not resolved, 
please let me know.
> I've briefly contacted the LKML, but after very little discussion the 
> issue was forgotten. I personally
> don't know how to solve the runtime boot problem while still enabling 
> kexec, but it was my hope
> that if the Fedora community were involved a solution might be found.
I had not tested the efi_ioremap fixes with kexec. I would appreciate 
testing feedback if you have any (test with kernel >= 2.6.29-rc8)


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