Messages in this thread Patch in this message | | | From | Denys Vlasenko <> | Subject | [PATCH] x86/kvm/emulate.c: simplify NOP (opcode 0x90) check | Date | Thu, 4 Jul 2013 10:58:29 +0200 |
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The check sits in switch() statement which itself can check for opcode 0x90 far more efficiently.
On assembler level, this change simply eliminates the following bit of code:
4c 8b a3 d8 00 00 00 mov 0xd8(%rbx),%r12 31 f6 xor %esi,%esi 48 89 df mov %rbx,%rdi e8 32 8c ff ff callq 490 <reg_read> 48 8d 83 78 01 00 00 lea 0x178(%rbx),%rax 83 8b 70 01 00 00 01 orl $0x1,0x170(%rbx) 83 8b 74 01 00 00 01 orl $0x1,0x174(%rbx) 49 39 c4 cmp %rax,%r12 0f 84 88 fa ff ff je 7304 <x86_emulate_insn+0x204>
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> CC: Paolo Bonzini <pbonzini@redhat.com> CC: Avi Kivity <avi.kivity@gmail.com> --- arch/x86/kvm/emulate.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 2bc1e81..7e6e74a 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4544,9 +4544,9 @@ special_insn: case 0x8d: /* lea r16/r32, m */ ctxt->dst.val = ctxt->src.addr.mem.ea; break; - case 0x90 ... 0x97: /* nop / xchg reg, rax */ - if (ctxt->dst.addr.reg == reg_rmw(ctxt, VCPU_REGS_RAX)) - break; + case 0x90: /* nop */ + break; + case 0x91 ... 0x97: /* xchg reg, rax */ rc = em_xchg(ctxt); break; case 0x98: /* cbw/cwde/cdqe */ -- 1.8.1.4
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