On Thu, 2008-02-14 at 13:06 +0100, Andi Kleen wrote: > > 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.
Because during early boot stage, alloc_page() is not available. If we do it there, we must make more pages executable to avoid alloc_page(). It may be acceptable for 2M mapping (aligned memory range with 2M), but I think it is not acceptable for 1G mapping (aligned memory range with 1G). Maybe it is the better method that always using the fixmap (efi_ioremap) to map executable memory area to avoid split large mapping. > > 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. This is the original method. The issue is that it must be synced with set_memory_*() and lookup_address() implementation. For example, it lacked 1G support when that is added to lookup_address(). Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
