linux.git/kernel/cpu.c, branch v4.9.158

Revert "x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation"

2018-11-23T11:57:41+00:00

This reverts commit 66fe51cb35d91d75a67ec8a38caf03da95e8c191 which is
commit 53c613fe6349994f023245519265999eed75957f upstream.

It's not ready for the stable trees as there are major slowdowns
involved with this patch.

Reported-by: Jiri Kosina 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Josh Poimboeuf 
Cc: Andrea Arcangeli 
Cc:  "WoodhouseDavid" 
Cc: Andi Kleen 
Cc: Tim Chen 
Cc:  "SchauflerCasey" 
Cc: Rainer Fiebig 
Signed-off-by: Greg Kroah-Hartman

x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

2018-11-13T19:16:47+00:00

commit 53c613fe6349994f023245519265999eed75957f upstream.

STIBP is a feature provided by certain Intel ucodes / CPUs. This feature
(once enabled) prevents cross-hyperthread control of decisions made by
indirect branch predictors.

Enable this feature if

- the CPU is vulnerable to spectre v2
- the CPU supports SMT and has SMT siblings online
- spectre_v2 mitigation autoselection is enabled (default)

After some previous discussion, this leaves STIBP on all the time, as wrmsr
on crossing kernel boundary is a no-no. This could perhaps later be a bit
more optimized (like disabling it in NOHZ, experiment with disabling it in
idle, etc) if needed.

Note that the synchronization of the mask manipulation via newly added
spec_ctrl_mutex is currently not strictly needed, as the only updater is
already being serialized by cpu_add_remove_lock, but let's make this a
little bit more future-proof.

Signed-off-by: Jiri Kosina 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Josh Poimboeuf 
Cc: Andrea Arcangeli 
Cc:  "WoodhouseDavid" 
Cc: Andi Kleen 
Cc: Tim Chen 
Cc:  "SchauflerCasey" 
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Non-SMP machines do not make use of booted_once

2018-08-15T16:14:55+00:00

commit 269777aa530f3438ec1781586cdac0b5fe47b061 upstream.

Commit 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
breaks non-SMP builds.

[ I suspect the 'bool' fields should just be made to be bitfields and be
  exposed regardless of configuration, but that's a separate cleanup
  that I'll leave to the owners of this file for later.   - Linus ]

Fixes: 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
Cc: Dave Hansen 
Cc: Thomas Gleixner 
Cc: Tony Luck 
Signed-off-by: Abel Vesa 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Fix SMT supported evaluation

2018-08-15T16:14:53+00:00

commit bc2d8d262cba5736332cbc866acb11b1c5748aa9 upstream

Josh reported that the late SMT evaluation in cpu_smt_state_init() sets
cpu_smt_control to CPU_SMT_NOT_SUPPORTED in case that 'nosmt' was supplied
on the kernel command line as it cannot differentiate between SMT disabled
by BIOS and SMT soft disable via 'nosmt'. That wreckages the state and
makes the sysfs interface unusable.

Rework this so that during bringup of the non boot CPUs the availability of
SMT is determined in cpu_smt_allowed(). If a newly booted CPU is not a
'primary' thread then set the local cpu_smt_available marker and evaluate
this explicitely right after the initial SMP bringup has finished.

SMT evaulation on x86 is a trainwreck as the firmware has all the
information _before_ booting the kernel, but there is no interface to query
it.

Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS")
Reported-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: detect SMT disabled by BIOS

2018-08-15T16:14:51+00:00

commit 73d5e2b472640b1fcdb61ae8be389912ef211bda upstream

If SMT is disabled in BIOS, the CPU code doesn't properly detect it.
The /sys/devices/system/cpu/smt/control file shows 'on', and the 'l1tf'
vulnerabilities file shows SMT as vulnerable.

Fix it by forcing 'cpu_smt_control' to CPU_SMT_NOT_SUPPORTED in such a
case.  Unfortunately the detection can only be done after bringing all
the CPUs online, so we have to overwrite any previous writes to the
variable.

Reported-by: Joe Mario 
Tested-by: Jiri Kosina 
Fixes: f048c399e0f7 ("x86/topology: Provide topology_smt_supported()")
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra 
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Set CPU_SMT_NOT_SUPPORTED early

2018-08-15T16:14:50+00:00

commit fee0aede6f4739c87179eca76136f83210953b86 upstream

The CPU_SMT_NOT_SUPPORTED state is set (if the processor does not support
SMT) when the sysfs SMT control file is initialized.

That was fine so far as this was only required to make the output of the
control file correct and to prevent writes in that case.

With the upcoming l1tf command line parameter, this needs to be set up
before the L1TF mitigation selection and command line parsing happens.

Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Josh Poimboeuf 
Link: https://lkml.kernel.org/r/20180713142323.121795971@linutronix.de
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Expose SMT control init function

2018-08-15T16:14:50+00:00

commit 8e1b706b6e819bed215c0db16345568864660393 upstream

The L1TF mitigation will gain a commend line parameter which allows to set
a combination of hypervisor mitigation and SMT control.

Expose cpu_smt_disable() so the command line parser can tweak SMT settings.

[ tglx: Split out of larger patch and made it preserve an already existing
  	force off state ]

Signed-off-by: Jiri Kosina 
Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Josh Poimboeuf 
Link: https://lkml.kernel.org/r/20180713142323.039715135@linutronix.de
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Online siblings when SMT control is turned on

2018-08-15T16:14:49+00:00

commit 215af5499d9e2b55f111d2431ea20218115f29b3 upstream

Writing 'off' to /sys/devices/system/cpu/smt/control offlines all SMT
siblings. Writing 'on' merily enables the abilify to online them, but does
not online them automatically.

Make 'on' more useful by onlining all offline siblings.

Signed-off-by: Thomas Gleixner 
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

x86/KVM: Warn user if KVM is loaded SMT and L1TF CPU bug being present

2018-08-15T16:14:47+00:00

commit 26acfb666a473d960f0fd971fe68f3e3ad16c70b upstream

If the L1TF CPU bug is present we allow the KVM module to be loaded as the
major of users that use Linux and KVM have trusted guests and do not want a
broken setup.

Cloud vendors are the ones that are uncomfortable with CVE 2018-3620 and as
such they are the ones that should set nosmt to one.

Setting 'nosmt' means that the system administrator also needs to disable
SMT (Hyper-threading) in the BIOS, or via the 'nosmt' command line
parameter, or via the /sys/devices/system/cpu/smt/control. See commit
05736e4ac13c ("cpu/hotplug: Provide knobs to control SMT").

Other mitigations are to use task affinity, cpu sets, interrupt binding,
etc - anything to make sure that _only_ the same guests vCPUs are running
on sibling threads.

Signed-off-by: Konrad Rzeszutek Wilk 
Signed-off-by: Thomas Gleixner 
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Boot HT siblings at least once

2018-08-15T16:14:47+00:00

commit 0cc3cd21657be04cb0559fe8063f2130493f92cf upstream

Due to the way Machine Check Exceptions work on X86 hyperthreads it's
required to boot up _all_ logical cores at least once in order to set the
CR4.MCE bit.

So instead of ignoring the sibling threads right away, let them boot up
once so they can configure themselves. After they came out of the initial
boot stage check whether its a "secondary" sibling and cancel the operation
which puts the CPU back into offline state.

[dwmw2: Backport to 4.9]

Reported-by: Dave Hansen 
Signed-off-by: Thomas Gleixner 
Tested-by: Tony Luck 
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman