Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [PATCH] x86: EFI runtime code mapping enhancement | Date | Thu, 14 Feb 2008 13:06:17 +0100 |
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> For EFI runtime service in virtual mode, using direct mapping is mainly > for kexec, where EFI runtime memory area need to be mapped at same > virtual address across kexec.
I see. I didn't consider this aspect.
> - Use direct mapping of kernel, clean NX bit from kernel page table > temporarily before/after EFI calling. This needs not split 2M page into > 4K pages, because the region changed is aligned with 2M. And, because > the changing is temporary, a little larger region is not a big issue.
I would just do it permanently.
> Aligning > EFI runtime code region with 1G seems not a good idea too. I think a > better method is adding a non-split mode to c_p_a(), where the region > changed is enlarged if necessary to avoid page allocation. This can be > used to implement early_set_memory_xx(). The early_set_memory_xx() > instead of duplicated c_p_a() variant can be used by EFI code.
I attempted something like this with my advisory vs required static protections last week, but it was rejected.
But yes having such a mode would make sense agreed.
The easiest way (as in least amount of code) to implement it actually is to just bypass set_memory_*() and just do the lookup_address() yourself and clear NX and do a global TLB flush. For the special case of NX that is fine because you don't need to worry about fixing up any aliases.
-Andi
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