RFC Emulator speedups - avoid initializations where possible

While initializing emulation context structure, kvm memsets to 0 a number of fields some of which are redundant since they get set eventually in x86_decode_insn. Cleanup unnecessary initializations and remove some fields.

This is on top of Paolo's RFC
KVM: x86: speedups for emulator memory accesses
https://lkml.org/lkml/2014/4/1/494

Here are the new realmode.flat numbers with improvement wrt unpatched kernel -

639 cycles/emulated jump instruction (4.3%) 776 cycles/emulated move instruction (7.5%) 791 cycles/emulated arithmetic instruction (11%) 943 cycles/emulated memory load instruction (5.2%) 948 cycles/emulated memory store instruction (7.6%) 929 cycles/emulated memory RMW instruction (9.0%)

v1 numbers -
639 cycles/emulated jump instruction
786 cycles/emulated move instruction
802 cycles/emulated arithmetic instruction
936 cycles/emulated memory load instruction
970 cycles/emulated memory store instruction
1000 cycles/emulated memory RMW instruction

v3:
Minor changes as proposed in review
- 3/6 - cleanup typos
- 6/6 - change comment in struct x86_emulate_ctxt and add back a missing if in decode_modrm

v2:
All thanks and credit to Paolo!
- 1/6 - no change
- 2/6 - new patch, inercept and check_perm replaced with checks for bits in ctxt->d
- 3/6 - new patch, remove if condition in decode_rm and rearrange bit operations
- 4/6 - remove else conditions from v1 and misc cleanups
- 5/6 - new patch, remove seg_override and related fields and functions
- 6/6 - new patch, remove memopp and move rip_relative to a local variable in decode_modrm

Bandan Das (6):
KVM: emulate: move init_decode_cache to emulate.c
KVM: emulate: Remove ctxt->intercept and ctxt->check_perm checks
KVM: emulate: cleanup decode_modrm
KVM: emulate: clean up initializations in init_decode_cache
KVM: emulate: rework seg_override
KVM: emulate: remove memopp and rip_relative

 arch/x86/include/asm/kvm_emulate.h | 26 +++++++-----
 arch/x86/kvm/emulate.c             | 85 ++++++++++++++++++--------------------
 arch/x86/kvm/x86.c                 | 13 ------
 3 files changed, 56 insertions(+), 68 deletions(-)

1.8.3.1