On Tue, Jan 29, 2019 at 04:37:08PM +0100, Heiko Carstens wrote: > On Tue, Jan 29, 2019 at 09:20:09AM +0100, Jiri Olsa wrote: > > On Tue, Jan 29, 2019 at 07:16:19AM +0100, Heiko Carstens wrote: > > > On Mon, Jan 28, 2019 at 10:14:58PM +0100, Jiri Olsa wrote: > > > > # cd /sys/kernel/debug/tracing > > > > # cat trace > > > > <...>-18602 [000] d... 288289.847945: do_sys_open: (do_sys_open+0x0/0x238) filename_string=(fault) > > > > <...>-18602 [000] d... 288289.848586: do_sys_open: (do_sys_open+0x0/0x238) filename_string=(fault) > > > > <...>-18602 [000] d... 288289.852643: do_sys_open: (do_sys_open+0x0/0x238) filename_string=(fault) > > > > <...>-18602 [000] d... 288289.853202: do_sys_open: (do_sys_open+0x0/0x238) filename_string=(fault) > > > > ... > > > > > > > > I'm getting this on latest upstream 5.0.0-rc3+ > > > > > > > > looks like we call strncpy_from_unsafe -> __get_user, which fails > > > > in this case.. any idea if this is perhaps some known issue on s390x? > > > > > > This looks like the wrong address space is accessed. The "string" type > > > is supposed to copy a string from _kernel_ space while the filename > > > argument of do_sys_open() is a user space pointer. > > > > > > This doesn't work on s390 due to the complete distinct address > > > spaces. At least that's what this looks like at a first glance. > > > > > > And if I'm correct it is not easy to "fix". _If_ this functionality is > > > desired then the kprobes interface must probably be changed so that it > > > would be possible to specify the address space from where something > > > should be copied. Or.. maybe the "__user" annotation in the kernel > > > code can be instrumented(?). > > > > > > > I see, I'd like to find out some more about this.. I found some docs in > > Documentation/s390, would you please point me to some other s390 docs? > > Well, there is only the architecture documentation. Not sure if you > really want to read this: > > http://publibfi.boulder.ibm.com/epubs/pdf/dz9zr011.pdf > > The relevant part is chapter 3 (Storage) - Address Spaces and Dynamic > Address Translation. > > However the short form is: s390 uses two address spaces. "Home Space" > for kernel address space and "Primary Address Space" for user space > (there are some special cases where this isn't true, but that doesn't > really matter here). > > Each address space has it's own(!) page tables. To access user space > from kernel space special instructions like MVCOS have to be used. > > Especially this means (unlike on other architectures) that you can't > tell from an address alone if it belongs to user space or kernel > space. > cool, thanks a lot for the info jirka
