MFC r336683:
Extend ranges of the critical sections to ensure that context switch
code never sees FPU pcb flags not consistent with the hardware state.

MFC r335072, r335089, r335131, r335132:
Enable eager FPU context switch on i386 and amd64.

CVE: CVE-2018-3665
Tested by: emaste (smoke boot)

MFC r325270:
Consistently ensure that we do not load MXCSR with reserved bits set.

MFC r313109:
Use ANSI definitions for some i386 functions.

MFC r294311:
Clear whole XMM register file instead of only XMM0. Also clear x87
registers. This brings amd64 on par with i386, providing consistent
initial FPU state.

PR: 206370

MFC r294312:
Use ANSI definitions. Wrap long line.

MFC r294313:
Adjust i386 comment to match amd64 one after r294311.

Approved by: re (gjb)

MFC r279936:
Remove write-only variable.

MFC 274817,274878,276801,276840,278976:
Improve support for XSAVE with debuggers.
- Dump an NT_X86_XSTATE note if XSAVE is in use. This note is designed
to match what Linux does in that 1) it dumps the entire XSAVE area
including the fxsave state, and 2) it stashes a copy of the current
xsave mask in the unused padding between the fxsave state and the
xstate header at the same location used by Linux.
- Teach readelf() to recognize NT_X86_XSTATE notes.
- Change PT_GET/SETXSTATE to take the entire XSAVE state instead of
only the extra portion. This avoids having to always make two
ptrace() calls to get or set the full XSAVE state.
- Add a PT_GET_XSTATE_INFO which returns the length of the current
XSTATE save area (so the size of the buffer needed for PT_GETXSTATE)
and the current XSAVE mask (%xcr0).

MFC 273988,273989,273995,274057:
MFamd64: Add support for extended FPU states on i386. This includes
support for AVX on i386.

MFC 270850,271053,271192,271717:
Save and restore FPU state across suspend and resume on i386.
- Create a separate structure for per-CPU state saved across suspend and
resume that is a superset of a pcb.
- Store the FPU state for suspend and resume in the new structure
(for amd64, this moves it out of the PCB)
- On both i386 and amd64, all of the FPU suspend/resume handling is now
done in C.

Approved by: re (hrs)

MFC r267767:
Add FPU_KERN_KTHR flag to fpu_kern_enter(9).
Apply the flag to padlock(4) and aesni(4).
In aesni_cipher_process(), do not leak FPU context state on error.

MFC r279936:
Remove write-only variable.

MFC 274817,274878,276801,276840,278976:
Improve support for XSAVE with debuggers.
- Dump an NT_X86_XSTATE note if XSAVE is in use. This note is designed
to match what Linux does in that 1) it dumps the entire XSAVE area
including the fxsave state, and 2) it stashes a copy of the current
xsave mask in the unused padding between the fxsave state and the
xstate header at the same location used by Linux.
- Teach readelf() to recognize NT_X86_XSTATE notes.
- Change PT_GET/SETXSTATE to take the entire XSAVE state instead of
only the extra portion. This avoids having to always make two
ptrace() calls to get or set the full XSAVE state.
- Add a PT_GET_XSTATE_INFO which returns the length of the current
XSTATE save area (so the size of the buffer needed for PT_GETXSTATE)
and the current XSAVE mask (%xcr0).

MFC 273988,273989,273995,274057:
MFamd64: Add support for extended FPU states on i386. This includes
support for AVX on i386.

MFC 270850,271053,271192,271717:
Save and restore FPU state across suspend and resume on i386.
- Create a separate structure for per-CPU state saved across suspend and
resume that is a superset of a pcb.
- Store the FPU state for suspend and resume in the new structure
(for amd64, this moves it out of the PCB)
- On both i386 and amd64, all of the FPU suspend/resume handling is now
done in C.

Approved by: re (hrs)

MFC r267767:
Add FPU_KERN_KTHR flag to fpu_kern_enter(9).
Apply the flag to padlock(4) and aesni(4).
In aesni_cipher_process(), do not leak FPU context state on error.