x86/configs: Add x86 debugging Kconfig fragment plus docs

The kernel has a wide variety of debugging options to help catch
and squash bugs.  However, new debugging is added all the time and
the existing options can be hard to find.

Add a Kconfig fragment with the debugging options which tip
maintainers expect to be used to test contributions.

This should make it easier for contributors to test their code and
find issues before submission.

  [ bp: Add to "make help" output, fix DEBUG_INFO selection as pointed
        out by Nathan Chancellor <nathan@kernel.org>. ]
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220331175728.299103A0@davehans-spike.ostc.intel.com

Documentation/process/maintainer-tip.rst

@@ -437,6 +437,20 @@ in a private repository which allows interested people to easily pull the
 series for testing. The usual way to offer this is a git URL in the cover
 letter of the patch series.
 
+Testing
+^^^^^^^
+
+Code should be tested before submitting to the tip maintainers.  Anything
+other than minor changes should be built, booted and tested with
+comprehensive (and heavyweight) kernel debugging options enabled.
+
+These debugging options can be found in kernel/configs/x86_debug.config
+and can be added to an existing kernel config by running:
+
+	make x86_debug.config
+
+Some of these options are x86-specific and can be left out when testing
+on other architectures.
 
 Coding style notes
 ------------------

arch/x86/Makefile

@@ -313,5 +313,6 @@ define archhelp
   echo  ''
   echo  '  kvm_guest.config	- Enable Kconfig items for running this kernel as a KVM guest'
   echo  '  xen.config		- Enable Kconfig items for running this kernel as a Xen guest'
+  echo  '  x86_debug.config	- Enable tip tree debugging options for testing'
 
 endef

kernel/configs/x86_debug.config

+CONFIG_X86_DEBUG_FPU=y
+CONFIG_LOCK_STAT=y
+CONFIG_DEBUG_VM=y
+CONFIG_DEBUG_VM_VMACACHE=y
+CONFIG_DEBUG_VM_RB=y
+CONFIG_DEBUG_SLAB=y
+CONFIG_DEBUG_KMEMLEAK=y
+CONFIG_DEBUG_PAGEALLOC=y
+CONFIG_SLUB_DEBUG_ON=y
+CONFIG_KMEMCHECK=y
+CONFIG_DEBUG_OBJECTS=y
+CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT=1
+CONFIG_GCOV_KERNEL=y
+CONFIG_LOCKDEP=y
+CONFIG_PROVE_LOCKING=y
+CONFIG_SCHEDSTATS=y
+CONFIG_VMLINUX_VALIDATION=y
+CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y