On 06/06/2014 01:58 PM, Matt Fleming wrote: > On 6 June 2014 21:37, H. Peter Anvin <hpa at zytor.com> wrote: >> >> OK... this is seriously problematic. >> >> #if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64) && \ >> !defined(CONFIG_EFI_MIXED) >> /* kernel/boot_param/ramdisk could be loaded above 4g */ >> # define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G >> #else >> # define XLF1 0 >> #endif >> >> The fact that even compiling with CONFIG_EFI_MIXED disables >> XLF_CAN_BE_LOADED_ABOVE_4G is really not going to fly. We should expect >> CONFIG_EFI_MIXED to be the norm, but *also* should expect that there is >> a legitimate need to load above 4G. >> >> Matt, could you explain why this is necessary? We need to figure out a >> way around this. >> >> My thinking is that disabling this flag is unnecessary, since a 32-bit >> EFI loader should not load above the 4G mark anyway, but if I'm confused >> and there is a more fundamental requirement, then we need to consider >> that more carefully. > > No, your comments are absolutely correct. I was the one who was > confused. I found this in the git history, > > commit 7d453eee36ae > Author: Matt Fleming <matt.fleming at intel.com> > Date: Fri Jan 10 18:52:06 2014 +0000 > > x86/efi: Wire up CONFIG_EFI_MIXED > > Add the Kconfig option and bump the kernel header version so that boot > loaders can check whether the handover code is available if they want. > > The xloadflags field in the bzImage header is also updated to reflect > that the kernel supports both entry points by setting both of > XLF_EFI_HANDOVER_32 and XLF_EFI_HANDOVER_64 when CONFIG_EFI_MIXED=y. > XLF_CAN_BE_LOADED_ABOVE_4G is disabled so that the kernel text is > guaranteed to be addressable with 32-bits. > > As you've pointed out above, a 32-bit loader is never going to load > the kernel above 4G, so we don't need to disable it. > > What's the best way to fix this up? Just undo the change from the above commit? > Yes, presumably (as a separate patch since the actual commit is quite large.) The patch needs to have a good description why the original patch was wrong. -hpa
