x86: Mark native_set_p4d() as __always_inline

x86: Mark native_set_p4d() as __always_inline

When CONFIG_OPTIMIZE_INLINING is enabled, the function native_set_p4d()
may not be fully inlined into the caller, resulting in a false-positive
warning about an access to the __pgtable_l5_enabled variable from a
non-__init function, despite the original caller being an __init function:

WARNING: vmlinux.o(.text.unlikely+0x1429): Section mismatch in reference from the function native_set_p4d() to the variable .init.data:__pgtable_l5_enabled
WARNING: vmlinux.o(.text.unlikely+0x1429): Section mismatch in reference from the function native_p4d_clear() to the variable .init.data:__pgtable_l5_enabled

The function native_set_p4d() references the variable __initdata
__pgtable_l5_enabled.  This is often because native_set_p4d lacks a
__initdata annotation or the annotation of __pgtable_l5_enabled is wrong.

Marking the native_set_p4d function and its caller native_p4d_clear()
avoids this problem.

I did not bisect the original cause, but I assume this is related to the
recent rework that turned pgtable_l5_enabled() into an inline function,
which in turn caused the compiler to make different inlining decisions.

Fixes: ad3fe525b950 ("x86/mm: Unify pgtable_l5_enabled usage in early boot code")
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]