From: gentoo guru contributors
Subject: [PATCH] x86/Kconfig: add x86_64 L1 cache shift fallback

XanMod adds X86_NATIVE_CPU to the x86-64 processor family choice.
Unlike concrete CPU family symbols, it does not match any default for
X86_L1_CACHE_SHIFT. If a config enables X86_NATIVE_CPU and does not
carry an old explicit cache-shift value, olddefconfig can leave
CONFIG_X86_L1_CACHE_SHIFT unset and derive CONFIG_X86_INTERNODE_CACHE_SHIFT=0.

Keep existing CPU-specific defaults first, including the NetBurst MPSC
case that uses 7, then fall back to 6 for otherwise unmatched x86_64
selections such as X86_NATIVE_CPU.

--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -694,6 +694,7 @@
 	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU || MK8SSE3 || MK10 || MBARCELONA || MBOBCAT || MJAGUAR || MBULLDOZER || MPILEDRIVER || MSTEAMROLLER || MEXCAVATOR || MZEN || MZEN2 || MZEN3 || MZEN4 || MZEN5 || MNEHALEM || MWESTMERE || MSILVERMONT || MGOLDMONT || MGOLDMONTPLUS || MSANDYBRIDGE || MIVYBRIDGE || MHASWELL || MBROADWELL || MSKYLAKE || MSKYLAKEX || MCANNONLAKE || MICELAKE_CLIENT || MICELAKE_SERVER || MCASCADELAKE || MCOOPERLAKE || MTIGERLAKE || MSAPPHIRERAPIDS || MROCKETLAKE || MALDERLAKE || MRAPTORLAKE || MMETEORLAKE || MEMERALDRAPIDS
 	default "4" if MELAN || M486SX || M486 || MGEODEGX1
 	default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
+	default "6" if X86_64
 
 config X86_F00F_BUG
 	def_bool y