x86/efi: Load fixmap GDT in efi_call_phys_epilog() before setting %cr3

Commit eeb89e2bb1ac ("x86/efi: Load fixmap GDT in efi_call_phys_epilog()")
moved loading the fixmap in efi_call_phys_epilog() after load_cr3() since
it was assumed to be more logical.

Turns out this is incorrect: In efi_call_phys_prolog(), the gdt with its
physical address is loaded first, and when the %cr3 is reloaded in _epilog
from initial_page_table to swapper_pg_dir again the gdt is no longer
mapped.  This results in a triple fault if an interrupt occurs after
load_cr3() and before load_fixmap_gdt(0). Calling load_fixmap_gdt(0) first
restores the execution order prior to commit eeb89e2bb1ac and fixes the
problem.

Fixes: eeb89e2bb1ac ("x86/efi: Load fixmap GDT in efi_call_phys_epilog()")
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: [email protected]
Cc: Andy Lutomirski <[email protected]>
Cc: Joerg Roedel <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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