linux.git/arch/x86/kernel/process.c, branch v6.0

Merge tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-08-01T16:49:29+00:00

Pull x86 cpu updates from Borislav Petkov:

 - Remove the vendor check when selecting MWAIT as the default idle
   state

 - Respect idle=nomwait when supplied on the kernel cmdline

 - Two small cleanups

* tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/cpu: Use MSR_IA32_MISC_ENABLE constants
  x86: Fix comment for X86_FEATURE_ZEN
  x86: Remove vendor checks from prefer_mwait_c1_over_halt
  x86: Handle idle=nomwait cmdline properly for x86_idle

x86/bugs: Optimize SPEC_CTRL MSR writes

2022-06-27T08:33:59+00:00

When changing SPEC_CTRL for user control, the WRMSR can be delayed
until return-to-user when KERNEL_IBRS has been enabled.

This avoids an MSR write during context switch.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value

2022-06-27T08:33:59+00:00

Due to TIF_SSBD and TIF_SPEC_IB the actual IA32_SPEC_CTRL value can
differ from x86_spec_ctrl_base. As such, keep a per-CPU value
reflecting the current task's MSR content.

  [jpoimboe: rename]

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86: Remove vendor checks from prefer_mwait_c1_over_halt

2022-06-08T20:00:19+00:00

Remove vendor checks from prefer_mwait_c1_over_halt function. Restore
the decision tree to support MWAIT C1 as the default idle state based on
CPUID checks as done by Thomas Gleixner in
commit 09fd4b4ef5bc ("x86: use cpuid to check MWAIT support for C1")

The decision tree is removed in
commit 69fb3676df33 ("x86 idle: remove mwait_idle() and "idle=mwait" cmdline param")

Prefer MWAIT when the following conditions are satisfied:
    1. CPUID_Fn00000001_ECX [Monitor] should be set
    2. CPUID_Fn00000005 should be supported
    3. If CPUID_Fn00000005_ECX [EMX] is set then there should be
       at least one C1 substate available, indicated by
       CPUID_Fn00000005_EDX [MWaitC1SubStates] bits.

Otherwise use HLT for default_idle function.

HPC customers who want to optimize for lower latency are known to
disable Global C-States in the BIOS. In fact, some vendors allow
choosing a BIOS 'performance' profile which explicitly disables
C-States.  In this scenario, the cpuidle driver will not be loaded and
the kernel will continue with the default idle state chosen at boot
time. On AMD systems currently the default idle state is HLT which has
a higher exit latency compared to MWAIT.

The reason for the choice of HLT over MWAIT on AMD systems is:

1. Families prior to 10h didn't support MWAIT
2. Families 10h-15h supported MWAIT, but not MWAIT C1. Hence it was
   preferable to use HLT as the default state on these systems.

However, AMD Family 17h onwards supports MWAIT as well as MWAIT C1. And
it is preferable to use MWAIT as the default idle state on these
systems, as it has lower exit latencies.

The below table represents the exit latency for HLT and MWAIT on AMD
Zen 3 system. Exit latency is measured by issuing a wakeup (IPI) to
other CPU and measuring how many clock cycles it took to wakeup.  Each
iteration measures 10K wakeups by pinning source and destination.

HLT:

25.0000th percentile  :      1900 ns
50.0000th percentile  :      2000 ns
75.0000th percentile  :      2300 ns
90.0000th percentile  :      2500 ns
95.0000th percentile  :      2600 ns
99.0000th percentile  :      2800 ns
99.5000th percentile  :      3000 ns
99.9000th percentile  :      3400 ns
99.9500th percentile  :      3600 ns
99.9900th percentile  :      5900 ns
  Min latency         :      1700 ns
  Max latency         :      5900 ns
Total Samples      9999

MWAIT:

25.0000th percentile  :      1400 ns
50.0000th percentile  :      1500 ns
75.0000th percentile  :      1700 ns
90.0000th percentile  :      1800 ns
95.0000th percentile  :      1900 ns
99.0000th percentile  :      2300 ns
99.5000th percentile  :      2500 ns
99.9000th percentile  :      3200 ns
99.9500th percentile  :      3500 ns
99.9900th percentile  :      4600 ns
  Min latency         :      1200 ns
  Max latency         :      4600 ns
Total Samples      9997

Improvement (99th percentile): 21.74%

Below is another result for context_switch2 micro-benchmark, which
brings out the impact of improved wakeup latency through increased
context-switches per second.

with HLT:
-------------------------------
50.0000th percentile  :  190184
75.0000th percentile  :  191032
90.0000th percentile  :  192314
95.0000th percentile  :  192520
99.0000th percentile  :  192844
MIN  :  190148
MAX  :  192852

with MWAIT:
-------------------------------
50.0000th percentile  :  277444
75.0000th percentile  :  278268
90.0000th percentile  :  278888
95.0000th percentile  :  279164
99.0000th percentile  :  280504
MIN  :  273278
MAX  :  281410

Improvement(99th percentile): ~ 45.46%

Signed-off-by: Wyes Karny 
Signed-off-by: Dave Hansen 
Acked-by: Peter Zijlstra (Intel) 
Tested-by: Zhang Rui 
Link: https://ozlabs.org/~anton/junkcode/context_switch2.c
Link: https://lkml.kernel.org/r/0cc675d8fd1f55e41b510e10abf2e21b6e9803d5.1654538381.git-series.wyes.karny@amd.com

x86: Handle idle=nomwait cmdline properly for x86_idle

2022-06-08T19:58:58+00:00

When kernel is booted with idle=nomwait do not use MWAIT as the
default idle state.

If the user boots the kernel with idle=nomwait, it is a clear
direction to not use mwait as the default idle state.
However, the current code does not take this into consideration
while selecting the default idle state on x86.

Fix it by checking for the idle=nomwait boot option in
prefer_mwait_c1_over_halt().

Also update the documentation around idle=nomwait appropriately.

[ dhansen: tweak commit message ]

Signed-off-by: Wyes Karny 
Signed-off-by: Dave Hansen 
Tested-by: Zhang Rui 
Link: https://lkml.kernel.org/r/fdc2dc2d0a1bc21c2f53d989ea2d2ee3ccbc0dbe.1654538381.git-series.wyes.karny@amd.com

Merge tag 'kthread-cleanups-for-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2022-06-03T23:03:05+00:00

Pull kthread updates from Eric Biederman:
 "This updates init and user mode helper tasks to be ordinary user mode
  tasks.

  Commit 40966e316f86 ("kthread: Ensure struct kthread is present for
  all kthreads") caused init and the user mode helper threads that call
  kernel_execve to have struct kthread allocated for them. This struct
  kthread going away during execve in turned made a use after free of
  struct kthread possible.

  Here, commit 343f4c49f243 ("kthread: Don't allocate kthread_struct for
  init and umh") is enough to fix the use after free and is simple
  enough to be backportable.

  The rest of the changes pass struct kernel_clone_args to clean things
  up and cause the code to make sense.

  In making init and the user mode helpers tasks purely user mode tasks
  I ran into two complications. The function task_tick_numa was
  detecting tasks without an mm by testing for the presence of
  PF_KTHREAD. The initramfs code in populate_initrd_image was using
  flush_delayed_fput to ensuere the closing of all it's file descriptors
  was complete, and flush_delayed_fput does not work in a userspace
  thread.

  I have looked and looked and more complications and in my code review
  I have not found any, and neither has anyone else with the code
  sitting in linux-next"

* tag 'kthread-cleanups-for-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  sched: Update task_tick_numa to ignore tasks without an mm
  fork: Stop allowing kthreads to call execve
  fork: Explicitly set PF_KTHREAD
  init: Deal with the init process being a user mode process
  fork: Generalize PF_IO_WORKER handling
  fork: Explicity test for idle tasks in copy_thread
  fork: Pass struct kernel_clone_args into copy_thread
  kthread: Don't allocate kthread_struct for init and umh

Merge tag 'x86_splitlock_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-05-24T02:24:47+00:00

Pull x86 splitlock updates from Borislav Petkov:

 - Add Raptor Lake to the set of CPU models which support splitlock

 - Make life miserable for apps using split locks by slowing them down
   considerably while the rest of the system remains responsive. The
   hope is it will hurt more and people will really fix their misaligned
   locks apps. As a result, free a TIF bit.

* tag 'x86_splitlock_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/split_lock: Enable the split lock feature on Raptor Lake
  x86/split-lock: Remove unused TIF_SLD bit
  x86/split_lock: Make life miserable for split lockers

Merge tag 'x86_core_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-05-24T01:42:07+00:00

Pull core x86 updates from Borislav Petkov:

 - Remove all the code around GS switching on 32-bit now that it is not
   needed anymore

 - Other misc improvements

* tag 'x86_core_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  bug: Use normal relative pointers in 'struct bug_entry'
  x86/nmi: Make register_nmi_handler() more robust
  x86/asm: Merge load_gs_index()
  x86/32: Remove lazy GS macros
  ELF: Remove elf_core_copy_kernel_regs()
  x86/32: Simplify ELF_CORE_COPY_REGS

Merge tag 'x86_cleanups_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-05-24T01:17:09+00:00

Pull x86 cleanups from Borislav Petkov:

 - Serious sanitization and cleanup of the whole APERF/MPERF and
   frequency invariance code along with removing the need for
   unnecessary IPIs

 - Finally remove a.out support

 - The usual trivial cleanups and fixes all over x86

* tag 'x86_cleanups_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
  x86: Remove empty files
  x86/speculation: Add missing srbds=off to the mitigations= help text
  x86/prctl: Remove pointless task argument
  x86/aperfperf: Make it correct on 32bit and UP kernels
  x86/aperfmperf: Integrate the fallback code from show_cpuinfo()
  x86/aperfmperf: Replace arch_freq_get_on_cpu()
  x86/aperfmperf: Replace aperfmperf_get_khz()
  x86/aperfmperf: Store aperf/mperf data for cpu frequency reads
  x86/aperfmperf: Make parts of the frequency invariance code unconditional
  x86/aperfmperf: Restructure arch_scale_freq_tick()
  x86/aperfmperf: Put frequency invariance aperf/mperf data into a struct
  x86/aperfmperf: Untangle Intel and AMD frequency invariance init
  x86/aperfmperf: Separate AP/BP frequency invariance init
  x86/smp: Move APERF/MPERF code where it belongs
  x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on_cpu()
  x86/process: Fix kernel-doc warning due to a changed function name
  x86: Remove a.out support
  x86/mm: Replace nodes_weight() with nodes_empty() where appropriate
  x86: Replace cpumask_weight() with cpumask_empty() where appropriate
  x86/pkeys: Remove __arch_set_user_pkey_access() declaration
  ...

x86/prctl: Remove pointless task argument

2022-05-13T10:56:28+00:00

The functions invoked via do_arch_prctl_common() can only operate on
the current task and none of these function uses the task argument.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Link: https://lore.kernel.org/r/87lev7vtxj.ffs@tglx