On Fri, Aug 17, 2012 at 03:43:56AM -0400, Tomas Racek wrote: > Well, I've added some debug statements to the code: > > void __init arch_init_ideal_nops(void) > { > switch (boot_cpu_data.x86_vendor) { > case X86_VENDOR_INTEL: > /* > * Due to a decoder implementation quirk, some > * specific Intel CPUs actually perform better with > * the "k8_nops" than with the SDM-recommended NOPs. > */ > if (boot_cpu_data.x86 == 6 && > boot_cpu_data.x86_model >= 0x0f && > boot_cpu_data.x86_model != 0x1c && > boot_cpu_data.x86_model != 0x26 && > boot_cpu_data.x86_model != 0x27 && > boot_cpu_data.x86_model < 0x30) { > printk("NOPS: Option 1\n"); > ideal_nops = k8_nops; > } else if (boot_cpu_has(X86_FEATURE_NOPL)) { > printk("NOPS: Option 2\n"); > ideal_nops = p6_nops; > } else { > printk("NOPS: Option 3\n"); > #ifdef CONFIG_X86_64 > ideal_nops = k8_nops; > #else > ideal_nops = intel_nops; > #endif > } > break; > default: > #ifdef CONFIG_X86_64 > ideal_nops = k8_nops; > #else > if (boot_cpu_has(X86_FEATURE_K8)) > ideal_nops = k8_nops; > else if (boot_cpu_has(X86_FEATURE_K7)) > ideal_nops = k7_nops; > else > ideal_nops = intel_nops; > #endif > } > } > > This gives me Option 1 with "-cpu host" and Option 2 without. This looks like an emulation bug. The interesting thing is that your both traces from the bugzilla point to generic_make_request_checks but it could also be due to timing. Decoding the instruction stream in the second trace in the bugzilla gives: [ 278.595106] Code: 03 48 89 03 48 8b 57 70 48 89 53 10 48 2b 01 8b 3f 48 89 45 98 48 8b 82 90 00 00 00 89 7d 94 48 8b 80 60 02 00 00 48 89 45 88 ac <17> 00 00 c8 45 85 e4 74 30 48 8b 43 10 48 8b 40 08 48 8b 40 48 All code ======== 0: 03 48 89 add -0x77(%rax),%ecx 3: 03 48 8b add -0x75(%rax),%ecx 6: 57 push %rdi 7: 70 48 jo 0x51 9: 89 53 10 mov %edx,0x10(%rbx) c: 48 2b 01 sub (%rcx),%rax f: 8b 3f mov (%rdi),%edi 11: 48 89 45 98 mov %rax,-0x68(%rbp) 15: 48 8b 82 90 00 00 00 mov 0x90(%rdx),%rax 1c: 89 7d 94 mov %edi,-0x6c(%rbp) 1f: 48 8b 80 60 02 00 00 mov 0x260(%rax),%rax 26: 48 89 45 88 mov %rax,-0x78(%rbp) 2a: ac lods %ds:(%rsi),%al 2b:* 17 (bad) <-- trapping instruction 2c: 00 00 add %al,(%rax) 2e: c8 45 85 e4 enterq $0x8545,$0xe4 32: 74 30 je 0x64 34: 48 8b 43 10 mov 0x10(%rbx),%rax 38: 48 8b 40 08 mov 0x8(%rax),%rax 3c: 48 8b 40 48 mov 0x48(%rax),%rax ... Code starting with the faulting instruction =========================================== 0: 17 (bad) 1: 00 00 add %al,(%rax) 3: c8 45 85 e4 enterq $0x8545,$0xe4 7: 74 30 je 0x39 9: 48 8b 43 10 mov 0x10(%rbx),%rax d: 48 8b 40 08 mov 0x8(%rax),%rax 11: 48 8b 40 48 mov 0x48(%rax),%rax and an instruction with opcode 0x17 in 64-bit mode is, AFAICT, invalid (on 32-bit it is "pop %ss" according to this thing: http://www.onlinedisassembler.com). -- Regards/Gruss, Boris. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html