Pull core x86 updates from Ingo Molnar:

 - The biggest change is the rework of the percpu code, to support the
   'Named Address Spaces' GCC feature, by Uros Bizjak:

      - This allows C code to access GS and FS segment relative memory
        via variables declared with such attributes, which allows the
        compiler to better optimize those accesses than the previous
        inline assembly code.

      - The series also includes a number of micro-optimizations for
        various percpu access methods, plus a number of cleanups of %gs
        accesses in assembly code.

      - These changes have been exposed to linux-next testing for the
        last ~5 months, with no known regressions in this area.

 - Fix/clean up __switch_to()'s broken but accidentally working handling
   of FPU switching - which also generates better code

 - Propagate more RIP-relative addressing in assembly code, to generate
   slightly better code

 - Rework the CPU mitigations Kconfig space to be less idiosyncratic, to
   make it easier for distros to follow & maintain these options

 - Rework the x86 idle code to cure RCU violations and to clean up the
   logic

 - Clean up the vDSO Makefile logic

 - Misc cleanups and fixes

* tag 'x86-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (52 commits)
  x86/idle: Select idle routine only once
  x86/idle: Let prefer_mwait_c1_over_halt() return bool
  x86/idle: Cleanup idle_setup()
  x86/idle: Clean up idle selection
  x86/idle: Sanitize X86_BUG_AMD_E400 handling
  sched/idle: Conditionally handle tick broadcast in default_idle_call()
  x86: Increase brk randomness entropy for 64-bit systems
  x86/vdso: Move vDSO to mmap region
  x86/vdso/kbuild: Group non-standard build attributes and primary object file rules together
  x86/vdso: Fix rethunk patching for vdso-image-{32,64}.o
  x86/retpoline: Ensure default return thunk isn't used at runtime
  x86/vdso: Use CONFIG_COMPAT_32 to specify vdso32
  x86/vdso: Use $(addprefix ) instead of $(foreach )
  x86/vdso: Simplify obj-y addition
  x86/vdso: Consolidate targets and clean-files
  x86/bugs: Rename CONFIG_RETHUNK              => CONFIG_MITIGATION_RETHUNK
  x86/bugs: Rename CONFIG_CPU_SRSO             => CONFIG_MITIGATION_SRSO
  x86/bugs: Rename CONFIG_CPU_IBRS_ENTRY       => CONFIG_MITIGATION_IBRS_ENTRY
  x86/bugs: Rename CONFIG_CPU_UNRET_ENTRY      => CONFIG_MITIGATION_UNRET_ENTRY
  x86/bugs: Rename CONFIG_SLS                  => CONFIG_MITIGATION_SLS
  ...

The idle routine selection is done on every CPU bringup operation and
has a guard in place which is effective after the first invocation,
which is a pointless exercise.

Invoke it once on the boot CPU and mark the related functions __init.
The guard check has to stay as xen_set_default_idle() runs early.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/87edcu6vaq.ffs@tglx

The return value is truly boolean. Make it so.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240229142248.518723854@linutronix.de

Updating the static call for x86_idle() from idle_setup() is
counter-intuitive.

Let select_idle_routine() handle it like the other idle choices, which
allows to simplify the idle selection later on.

While at it rewrite comments and return a proper error code and not -1.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240229142248.455616019@linutronix.de

Clean up the code to make it readable. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240229142248.392017685@linutronix.de

amd_e400_idle(), the idle routine for AMD CPUs which are affected by
erratum 400 violates the RCU constraints by invoking tick_broadcast_enter()
and tick_broadcast_exit() after the core code has marked RCU non-idle.  The
functions can end up in lockdep or tracing, which rightfully triggers a
RCU warning.

The core code provides now a static branch conditional invocation of the
broadcast functions.

Remove amd_e400_idle(), enforce default_idle() and enable the static branch
on affected CPUs to cure this.

  [ bp: Fold in a fix for a IS_ENABLED() check fail missing a "CONFIG_"
    prefix which tglx spotted. ]

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/877cim6sis.ffs@tglx

In commit c1d171a00294 ("x86: randomize brk"), arch_randomize_brk() was
defined to use a 32MB range (13 bits of entropy), but was never increased
when moving to 64-bit. The default arch_randomize_brk() uses 32MB for
32-bit tasks, and 1GB (18 bits of entropy) for 64-bit tasks.

Update x86_64 to match the entropy used by arm64 and other 64-bit
architectures.

Reported-by: y0un9n132@gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Jiri Kosina <jkosina@suse.com>
Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@mail.gmail.com/
Link: https://lore.kernel.org/r/20240217062545.1631668-1-keescook@chromium.org

It's really a non-intuitive name. Rename it to __max_threads_per_core which
is obvious.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240213210253.011307973@linutronix.de

Fix typos, most reported by "codespell arch/x86".  Only touches comments,
no code changes.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20240103004011.1758650-1-helgaas@kernel.org

When clone fails after the shadow stack is allocated, any allocated shadow
stack is cleaned up in exit_thread() in copy_process(). So the logic in
copy_thread() is unneeded, and also will not handle failures that happen
outside of copy_thread().

In addition, since there is a second attempt to unmap the same shadow
stack, there is a race where an newly mapped region could get unmapped.

So remove the logic in copy_thread() and rely on exit_thread() to handle
clone failure.

Fixes: b2926a36b97a ("x86/shstk: Handle thread shadow stack")
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: H.J. Lu <hjl.tools@gmail.com>
Link: https://lore.kernel.org/all/20230908203655.543765-3-rick.p.edgecombe%40intel.com