linux.git/arch/x86/kernel/process_64.c, branch v5.6

x86: Remove force_iret()

2020-01-08T18:40:51+00:00

force_iret() was originally intended to prevent the return to user mode with
the SYSRET or SYSEXIT instructions, in cases where the register state could
have been changed to be incompatible with those instructions.  The entry code
has been significantly reworked since then, and register state is validated
before SYSRET or SYSEXIT are used.  force_iret() no longer serves its original
purpose and can be eliminated.

Signed-off-by: Brian Gerst 
Signed-off-by: Borislav Petkov 
Acked-by: Oleg Nesterov 
Link: https://lkml.kernel.org/r/20191219115812.102620-1-brgerst@gmail.com

x86/iopl: Remove legacy IOPL option

2019-11-16T10:24:05+00:00

The IOPL emulation via the I/O bitmap is sufficient. Remove the legacy
cruft dealing with the (e)flags based IOPL mechanism.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Juergen Gross  (Paravirt and Xen parts)
Acked-by: Andy Lutomirski

x86/process: Unify copy_thread_tls()

2019-11-16T10:23:59+00:00

While looking at the TSS io bitmap it turned out that any change in that
area would require identical changes to copy_thread_tls(). The 32 and 64
bit variants share sufficient code to consolidate them into a common
function to avoid duplication of upcoming modifications.

Signed-off-by: Thomas Gleixner 
Acked-by: Andy Lutomirski

x86/process: Delete useless check for dead process with LDT

2019-07-16T22:42:27+00:00

At release_thread(), ->mm is NULL; and it is fine for the former mm to
still have an LDT. Delete this check in process_64.c, similar to
commit 2684927c6b93 ("[PATCH] x86: Deprecate useless bug"), which did the
same in process_32.c.

Signed-off-by: Jann Horn 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190712224152.13129-1-jannh@google.com

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

Merge branch 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-05-07T17:24:10+00:00

Pull x86 FPU state handling updates from Borislav Petkov:
 "This contains work started by Rik van Riel and brought to fruition by
  Sebastian Andrzej Siewior with the main goal to optimize when to load
  FPU registers: only when returning to userspace and not on every
  context switch (while the task remains in the kernel).

  In addition, this optimization makes kernel_fpu_begin() cheaper by
  requiring registers saving only on the first invocation and skipping
  that in following ones.

  What is more, this series cleans up and streamlines many aspects of
  the already complex FPU code, hopefully making it more palatable for
  future improvements and simplifications.

  Finally, there's a __user annotations fix from Jann Horn"

* 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (29 commits)
  x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails
  x86/pkeys: Add PKRU value to init_fpstate
  x86/fpu: Restore regs in copy_fpstate_to_sigframe() in order to use the fastpath
  x86/fpu: Add a fastpath to copy_fpstate_to_sigframe()
  x86/fpu: Add a fastpath to __fpu__restore_sig()
  x86/fpu: Defer FPU state load until return to userspace
  x86/fpu: Merge the two code paths in __fpu__restore_sig()
  x86/fpu: Restore from kernel memory on the 64-bit path too
  x86/fpu: Inline copy_user_to_fpregs_zeroing()
  x86/fpu: Update xstate's PKRU value on write_pkru()
  x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD
  x86/fpu: Always store the registers in copy_fpstate_to_sigframe()
  x86/entry: Add TIF_NEED_FPU_LOAD
  x86/fpu: Eager switch PKRU state
  x86/pkeys: Don't check if PKRU is zero before writing it
  x86/fpu: Only write PKRU if it is different from current
  x86/pkeys: Provide *pkru() helpers
  x86/fpu: Use a feature number instead of mask in two more helpers
  x86/fpu: Make __raw_xsave_addr() use a feature number instead of mask
  x86/fpu: Add an __fpregs_load_activate() internal helper
  ...

x86/fpu: Defer FPU state load until return to userspace

2019-04-12T17:34:47+00:00

Defer loading of FPU state until return to userspace. This gives
the kernel the potential to skip loading FPU state for tasks that
stay in kernel mode, or for tasks that end up with repeated
invocations of kernel_fpu_begin() & kernel_fpu_end().

The fpregs_lock/unlock() section ensures that the registers remain
unchanged. Otherwise a context switch or a bottom half could save the
registers to its FPU context and the processor's FPU registers would
became random if modified at the same time.

KVM swaps the host/guest registers on entry/exit path. This flow has
been kept as is. First it ensures that the registers are loaded and then
saves the current (host) state before it loads the guest's registers. The
swap is done at the very end with disabled interrupts so it should not
change anymore before theg guest is entered. The read/save version seems
to be cheaper compared to memcpy() in a micro benchmark.

Each thread gets TIF_NEED_FPU_LOAD set as part of fork() / fpu__copy().
For kernel threads, this flag gets never cleared which avoids saving /
restoring the FPU state for kernel threads and during in-kernel usage of
the FPU registers.

 [
   bp: Correct and update commit message and fix checkpatch warnings.
   s/register/registers/ where it is used in plural.
   minor comment corrections.
   remove unused trace_x86_fpu_activate_state() TP.
 ]

Signed-off-by: Rik van Riel 
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: Konrad Rzeszutek Wilk 
Cc: kvm ML 
Cc: Nicolai Stange 
Cc: Paolo Bonzini 
Cc: "Radim Krčmář" 
Cc: Tim Chen 
Cc: Waiman Long 
Cc: x86-ml 
Cc: Yi Wang 
Link: https://lkml.kernel.org/r/20190403164156.19645-24-bigeasy@linutronix.de

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: Remove fpu__restore()

2019-04-09T17:27:42+00:00

There are no users of fpu__restore() so it is time to remove it. The
comment regarding fpu__restore() and TS bit is stale since commit

  b3b0870ef3ffe ("i387: do not preload FPU state at task switch time")

and has no meaning since.

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: Jonathan Corbet 
Cc: kvm ML 
Cc: linux-doc@vger.kernel.org
Cc: Nicolai Stange 
Cc: Paolo Bonzini 
Cc: Radim Krčmář 
Cc: Rik van Riel 
Cc: x86-ml 
Link: https://lkml.kernel.org/r/20190403164156.19645-3-bigeasy@linutronix.de

sched/x86_64: Don't save flags on context switch

2019-04-03T09:02:24+00:00

Now that we have objtool validating AC=1 state for all x86_64 code,
we can once again guarantee clean flags on schedule.

Signed-off-by: Peter Zijlstra (Intel) 
Cc: Borislav Petkov 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar