linux.git/arch/x86/kernel/fpu/init.c, branch v5.14

x86/fpu: Get rid of fpu__get_supported_xfeatures_mask()

2021-06-23T15:49:46+00:00

This function is really not doing what the comment advertises:

 "Find supported xfeatures based on cpu features and command-line input.
  This must be called after fpu__init_parse_early_param() is called and
  xfeatures_mask is enumerated."

fpu__init_parse_early_param() does not exist anymore and the function just
returns a constant.

Remove it and fix the caller and get rid of further references to
fpu__init_parse_early_param().

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210623121451.816404717@linutronix.de

x86/fpu: Mark various FPU state variables __ro_after_init

2021-06-23T15:49:45+00:00

Nothing modifies these after booting.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Reviewed-by: Andy Lutomirski 
Link: https://lkml.kernel.org/r/20210623121451.611751529@linutronix.de

x86/fpu: Handle FPU-related and clearcpuid command line arguments earlier

2020-09-21T22:24:27+00:00

FPU initialization handles them currently. However, in the case
of clearcpuid=, some other early initialization code may check for
features before the FPU initialization code is called. Handling the
argument earlier allows the command line to influence those early
initializations.

Signed-off-by: Mike Hommey 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20200921215638.37980-1-mh@glandium.org

x86/fpu: Allow multiple bits in clearcpuid= parameter

2020-09-10T16:32:05+00:00

Commit

  0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE argument")

changed clearcpuid parsing from __setup() to cmdline_find_option().
While the __setup() function would have been called for each clearcpuid=
parameter on the command line, cmdline_find_option() will only return
the last one, so the change effectively made it impossible to disable
more than one bit.

Allow a comma-separated list of bit numbers as the argument for
clearcpuid to allow multiple bits to be disabled again. Log the bits
being disabled for informational purposes.

Also fix the check on the return value of cmdline_find_option(). It
returns -1 when the option is not found, so testing as a boolean is
incorrect.

Fixes: 0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE argument")
Signed-off-by: Arvind Sankar 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20200907213919.2423441-1-nivedita@alum.mit.edu

x86/fpu/xstate: Define new macros for supervisor and user xstates

2020-05-12T18:34:38+00:00

XCNTXT_MASK is 'all supported xfeatures' before introducing supervisor
xstates.  Rename it to XFEATURE_MASK_USER_SUPPORTED to make clear that
these are user xstates.

Replace XFEATURE_MASK_SUPERVISOR with the following:
- XFEATURE_MASK_SUPERVISOR_SUPPORTED: Currently nothing.  ENQCMD and
  Control-flow Enforcement Technology (CET) will be introduced in separate
  series.
- XFEATURE_MASK_SUPERVISOR_UNSUPPORTED: Currently only Processor Trace.
- XFEATURE_MASK_SUPERVISOR_ALL: the combination of above.

Co-developed-by: Yu-cheng Yu 
Signed-off-by: Fenghua Yu 
Signed-off-by: Yu-cheng Yu 
Signed-off-by: Borislav Petkov 
Reviewed-by: Dave Hansen 
Reviewed-by: Tony Luck 
Link: https://lkml.kernel.org/r/20200512145444.15483-3-yu-cheng.yu@intel.com

x86/fpu: Inline fpu__xstate_clear_all_cpu_caps()

2019-07-07T10:01:47+00:00

All fpu__xstate_clear_all_cpu_caps() does is to invoke one simple
function since commit

  73e3a7d2a7c3b ("x86/fpu: Remove the explicit clearing of XSAVE dependent features")

so invoke that function directly and remove the wrapper.

Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190704060743.rvew4yrjd6n33uzx@linutronix.de

x86/fpu: Make 'no387' and 'nofxsr' command line options useful

2019-07-07T10:01:46+00:00

The command line option `no387' is designed to disable the FPU
entirely. This only 'works' with CONFIG_MATH_EMULATION enabled.

But on 64bit this cannot work because user space expects SSE to work which
required basic FPU support. MATH_EMULATION does not help because SSE is not
emulated.

The command line option `nofxsr' should also be limited to 32bit because
FXSR is part of the required flags on 64bit so turning it off is not
possible.

Clearing X86_FEATURE_FPU without emulation enabled will not work anyway and
hang in fpu__init_system_early_generic() before the console is enabled.

Setting additioal dependencies, ensures that the CPU still boots on a
modern CPU. Otherwise, dropping FPU will leave FXSR enabled causing the
kernel to crash early in fpu__init_system_mxcsr().

With XSAVE support it will crash in fpu__init_cpu_xstate(). The problem is
that xsetbv() with XMM set and SSE cleared is not allowed.  That means
XSAVE has to be disabled. The XSAVE support is disabled in
fpu__init_system_xstate_size_legacy() but it is too late. It can be
removed, it has been added in commit

  1f999ab5a1360 ("x86, xsave: Disable xsave in i387 emulation mode")

to use `no387' on a CPU with XSAVE support.

All this happens before console output.

After hat, the next possible crash is in RAID6 detect code because MMX
remained enabled. With a 3DNOW enabled config it will explode in memcpy()
for instance due to kernel_fpu_begin() but this is unconditionally enabled.

This is enough to boot a Debian Wheezy on a 32bit qemu "host" CPU which
supports everything up to XSAVES, AVX2 without 3DNOW. Later, Debian
increased the minimum requirements to i686 which means it does not boot
userland atleast due to CMOV.

After masking the additional features it still keeps SSE4A and 3DNOW*
enabled (if present on the host) but those are unused in the kernel.

Restrict `no387' and `nofxsr' otions to 32bit only. Add dependencies for
FPU, FXSR to additionaly mask CMOV, MMX, XSAVE if FXSR or FPU is cleared.

Reported-by: Vegard Nossum 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190703083247.57kjrmlxkai3vpw3@linutronix.de

treewide: Add SPDX license identifier for missed files

2019-05-21T08:50:45+00:00

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have EXPORT_.*_SYMBOL_GPL inside which was used in the
   initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

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

x86/fpu: Remove fpu->initialized

2019-04-10T13:42:40+00:00

The struct fpu.initialized member is always set to one for user tasks
and zero for kernel tasks. This avoids saving/restoring the FPU
registers for kernel threads.

The ->initialized = 0 case for user tasks has been removed in previous
changes, for instance, by doing an explicit unconditional init at fork()
time for FPU-less systems which was otherwise delayed until the emulated
opcode.

The context switch code (switch_fpu_prepare() + switch_fpu_finish())
can't unconditionally save/restore registers for kernel threads. Not
only would it slow down the switch but also load a zeroed xcomp_bv for
XSAVES.

For kernel_fpu_begin() (+end) the situation is similar: EFI with runtime
services uses this before alternatives_patched is true. Which means that
this function is used too early and it wasn't the case before.

For those two cases, use current->mm to distinguish between user and
kernel thread. For kernel_fpu_begin() skip save/restore of the FPU
registers.

During the context switch into a kernel thread don't do anything. There
is no reason to save the FPU state of a kernel thread.

The reordering in __switch_to() is important because the current()
pointer needs to be valid before switch_fpu_finish() is invoked so ->mm
is seen of the new task instead the old one.

N.B.: fpu__save() doesn't need to check ->mm because it is called by
user tasks only.

 [ bp: Massage. ]

Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Borislav Petkov 
Reviewed-by: Dave Hansen 
Reviewed-by: Thomas Gleixner 
Cc: Andy Lutomirski 
Cc: Aubrey Li 
Cc: Babu Moger 
Cc: "Chang S. Bae" 
Cc: Dmitry Safonov 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jann Horn 
Cc: "Jason A. Donenfeld" 
Cc: Joerg Roedel 
Cc: kvm ML 
Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Nicolai Stange 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Radim Krčmář 
Cc: Rik van Riel 
Cc: Sergey Senozhatsky 
Cc: Will Deacon 
Cc: x86-ml 
Link: https://lkml.kernel.org/r/20190403164156.19645-8-bigeasy@linutronix.de

x86/fpu: Parse clearcpuid= as early XSAVE argument

2017-10-17T15:14:57+00:00

With a followon patch we want to make clearcpuid affect the XSAVE
configuration. But xsave is currently initialized before arguments
are parsed. Move the clearcpuid= parsing into the special
early xsave argument parsing code.

Since clearcpuid= contains a = we need to keep the old __setup
around as a dummy, otherwise it would end up as a environment
variable in init's environment.

Signed-off-by: Andi Kleen 
Reviewed-by: Thomas Gleixner 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/20171013215645.23166-4-andi@firstfloor.org
Signed-off-by: Ingo Molnar