On 04/08/2016 11:44 PM, Andy Lutomirski wrote:
Feel free to ask for help on some of these details. user_64bit_mode will be helpful too.
Hello again, here are some questions on TIF_IA32 removal: - in function intel_pmu_pebs_fixup_ip: there is need to know if process was it native/compat mode for instruction interpreter for IP + one instruction fixup. There are registers, but they are from PEBS, which does not contain segment descriptors (even for PEBSv3). Other values are from interrupt regs (look at setup_pebs_sample_data). So, I guess, we may use user_64bit_mode on interrupt register set, which will be racy with changing task's mode, but quite ok? - the same with LBR branching: I may got cs value for user_64bit_mode or all registers set from intel_pmu_handle_irq and pass it through intel_pmu_lbr_read => intel_pmu_lbr_filter to branch_type for instruction decoder, which may missinterpret opcode for the same racy-mode-switching app. Is it also fine? - for coredumping/ptracing, I will change test_thread_flag(TIF_IA32) by user_64bit_mode(task_pt_regs()) - that looks/should be simple. It's also valid as at the moment of coredump or of PTRACE_GETREGSET task isn't running. - I do not know what to do with uprobes - as you noted, the way it cheks ia32_compat is buggy even now: task that switches CS to __USER32_CS or back to __USER_CS will have lousy inserted uprobe in mm. So, how do we know on insert-time, with which descriptor will be program on uprobed code? - for MPX, I guess, tracking which syscall called mpx_enable_management will work, at least it may be documented, that before switching, one need to disable mpx. - perf_reg_abi everywhere is used with current, so it's also simple-switching to user_64bit_mode(task_pt_regs(current)). For the conclusion: I will send those patches, but I do not know what to do with uprobes tracing. Could you give an advice what to do with that? It seems like, if I do those things, I will only need a way to change vdso blob, without swapping some compatible flags, as 64-bit tasks will differ from 32-bit only by the way they execute syscalls. -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
