Am 02.03.2015 um 18:18 schrieb Mike Frysinger: > On 02 Mar 2015 09:56, Christian Borntraeger wrote: >> Am 28.02.2015 um 22:24 schrieb Mike Frysinger: >>> when running strace tests, we noticed that si_addr appears to be wrong. the >>> attached test shows the problem -- si_addr isn't set to the faulting address. >>> >>> i hacked arch/s390/mm/fault.c:do_sigsegv to load regs->psw.addr (sans mask), >>> and it worked for insn based crashes. but obviously that doesn't work for >>> data based ones. i'm not familiar with how regs->int_parm_long works though, >>> so maybe it's supposed to be loaded indirectly. the use of __FAIL_ADDR_MASK >>> blindly is most certainly incorrect ... >>> >>> whatever the fix, do_sigbus probably needs it too. >> >> The problem is that all faults on s390 give the address only on page >> granularity (HW-wise) >> e.g. if you use 0x123456 as fail address you get si_addr == 0x123000 > > can't you detect when the fault is data-vs-code access ? you could at least > make the code fault exact. > -mike There is no indication which part caused the fault. Worst case: there can be 3 sources: instruction address, address1 and address 2 (for example the MVC instruction). Now, we could start with "guessing", but what happens if 2 or 3 of the addresses are in the same page (e.g. some trampoline code on the stack). Or we could start walking page tables: this would require us to decode ~1000 instructions just to race against other kernel code that does invalidation, e.g. vmscan/swap. IMHO the proper solution is to accept that translation faults are on the page, unless the maintainers Martin or Heiko have a clever idea. Christian PS: Programs that need the fault address might need special handling. For an example have a look at valgrind: https://github.com/svn2github/valgrind/blob/master/coregrind/m_signals.c line 2385 fault_mask -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
