On Wednesday 11 February 2015 21:40:33 Nishanth Menon wrote: > On Wed, Feb 11, 2015 at 2:28 PM, Pali Rohár <pali.rohar@xxxxxxxxx> wrote: > > On Wednesday 11 February 2015 16:22:51 Matthijs van Duin wrote: > >> On 11 February 2015 at 13:39, Pali Rohár > >> <pali.rohar@xxxxxxxxx> > > > > wrote: > >> >> Anyhow, since checking the firewalls/APs to see if you > >> >> have permission will probably only get you yet another > >> >> fault if things are walled off, the robust way of > >> >> dealing with this sort of situation is by probing the > >> >> device with a read while trapping bus faults. This also > >> >> handles modules that are unreachable for other reasons, > >> >> e.g. being disabled by eFuse. > >> > > >> > It is possible to patch kernel code to mask or ignore > >> > that fault? Can you help me with something like that? > >> > >> As I mentioned, I'm still learning my way around the > >> kernel, so I don't feel very comfortable suggesting a > >> concrete patch just yet. I've been browsing arch/arm/mm/ > >> however and my impression is that all that would be > >> required is editing fault.c by making a copy of do_bad but > >> containing > >> > >> return user_mode(regs) || !fixup_exception(regs); > >> > >> and hook it onto the appropriate fault codes. However, > >> this really needs the opinion of someone more familiar > >> with this code. > >> > >> I do have an observation to make on the issue of fault > >> decoding: the list in fsr-2level.c may be "standard ARMv3 > >> and ARMv4 aborts" but they are quite wrong for ARMv7 which > >> has: > >> > >> [ 0] - > >> [ 1] alignment fault > >> [ 2] debug event > >> [ 3] section access flag fault > >> [ 4] instruction cache maintainance fault (reported via > >> data abort) [ 5] section translation fault > >> [ 6] page access flag fault > >> [ 7] page translation fault > >> [ 8] bus error on access > >> [ 9] section domain fault > >> [10] - > >> [11] page domain fault > >> [12] bus error on section table walk > >> [13] section permission fault > >> [14] bus error on page table walk > >> [15] page permission fault > >> [16] (TLB conflict abort) > >> [17] - > >> [18] - > >> [19] - > >> [20] (lockdown abort) > >> [21] - > >> [22] async bus error (reported via data abort) > >> [23] - > >> [24] async parity/ECC error (reported via data abort) > >> [25] parity/ECC error on access > >> [26] (coprocessor abort) > >> [27] - > >> [28] parity/ECC error on section table walk > >> [29] - > >> [30] parity/ECC error on page table walk > >> [31] - > >> > >> Some entries are patched up near the bottom of fault.c but > >> many bogus messages remain, for example the "on linefetch" > >> vs "on non-linefetch" is misleading since no such thing > >> can be inferred from the fault status on v7. Also, the > >> i-cache maintenance fault handling looks wrong to me: it > >> should fetch the actual fault status from IFSR (even > >> though the address still comes from DFSR) and dispatch > >> based on that. > >> > >> Async external aborts (async bus error and async parity/ECC > >> error) give you basically no info. DFAR will contain > >> garbage hence displaying it will confuse rather than > >> enlighten, a traceback is pointless since the instruction > >> that caused the access is long retired, likewise > >> user_mode() doesn't matter since a transition to kernel > >> space may have happened after the access that cause the > >> abort. Basically they should be treated more as an IRQ > >> than as a fault (note they can also be masked just like > >> irqs). In case of a bus error, it may be appropriate to > >> just warn about it, or perhaps send a signal to the > >> current process, although in the latter case it should > >> have some means to distinguish it from a synchronous bus > >> error. > >> > >> At least on the cortex-a8, a parity/ECC error (whether > >> async or not) is to be regarded as absolutely fatal. > >> Quoth the TRM: "No recovery is possible. The abort handler > >> must disable the caches, communicate the fail directly > >> with the external system, request a reboot." > >> > >> Bit 10 no longer indicates an asynchronous (let alone > >> imprecise) fault. Apart from the debug events and async > >> aborts (and possibly some implementation-defined aborts), > >> all aborts listed are synchronous, and DFAR/IFAR is valid. > >> There's no technical obstruction to make these trappable > >> via the kernel exception handling mechanism. (Though at > >> least in case of parity/ECC errors one shouldn't.) > > > > Tony, Nishanth, or somebody else... can you help with memory > > management? Or do you know some expert for arch/arm/mm/ > > code? > > Folks in linux-arm-kernel are probably the right people, I > suppose. Looping them in. Hi folks in linux-arm-kernel! Can you help us with above problem? How to catch external abort on non-linefetch in kernel driver and prevent kernel panic? Here is that kernel panic log: http://thread.gmane.org/gmane.linux.ports.arm.omap/108397/ We want to check for "Unhandled fault: external abort on non- linefetch" and if it happens disable some functionality in kernel driver omap-aes.ko -- Pali Rohár pali.rohar@xxxxxxxxx
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