linux-kernel - Re: qemu-arm64: handle_futex_death - kernel/futex/core.c:661 - Unable to handle kernel unknown 43 at virtual address

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Message-ID: <CAMj1kXE8VrG6aPsjByd83kavw7He6vn=DszhJfAd-TfP9y8VBA@mail.gmail.com>
Date:   Thu, 26 Oct 2023 17:39:11 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        lkft-triage@...ts.linaro.org, Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        LTP List <ltp@...ts.linux.it>, Petr Vorel <pvorel@...e.cz>
Subject: Re: qemu-arm64: handle_futex_death - kernel/futex/core.c:661 - Unable
 to handle kernel unknown 43 at virtual address

On Thu, 26 Oct 2023 at 17:30, Mark Rutland <mark.rutland@....com> wrote:
>
> On Thu, Oct 26, 2023 at 08:11:26PM +0530, Naresh Kamboju wrote:
> > Following kernel crash noticed on qemu-arm64 while running LTP syscalls
> > set_robust_list test case running Linux next 6.6.0-rc7-next-20231026 and
> > 6.6.0-rc7-next-20231025.
> >
> > BAD: next-20231025
> > Good: next-20231024
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> > Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
> >
> > Log:
> > ----
> > <1>[  203.119139] Unable to handle kernel unknown 43 at virtual
> > address 0001ffff9e2e7d78
> > <1>[  203.119838] Mem abort info:
> > <1>[  203.120064]   ESR = 0x000000009793002b
> > <1>[  203.121040]   EC = 0x25: DABT (current EL), IL = 32 bits
> > set_robust_list01    1  TPASS  :  set_robust_list: retval = -1
> > (expected -1), errno = 22 (expected 22)
> > set_robust_list01    2  TPASS  :  set_robust_list: retval = 0
> > (expected 0), errno = 0 (expected 0)
> > <1>[  203.124496]   SET = 0, FnV = 0
> > <1>[  203.124778]   EA = 0, S1PTW = 0
> > <1>[  203.125029]   FSC = 0x2b: unknown 43
>
> It looks like this is fallout from the LPA2 enablement.
>
> According to the latest ARM ARM (ARM DDI 0487J.a), page D19-6475, that "unknown
> 43" (0x2b / 0b101011) is the DFSC for a level -1 translation fault:
>
>         0b101011 When FEAT_LPA2 is implemented:
>                  Translation fault, level -1.
>
> It's triggered here by an LDTR in a get_user() on a bogus userspace address.
> The exception is expected, and it's supposed to be handled via the exception
> fixups, but the LPA2 patches didn't update the fault_info table entries for all
> the level -1 faults, and so those all get handled by do_bad() and don't call
> fixup_exception(), causing them to be fatal.
>
> It should be relatively simple to update the fault_info table for the level -1
> faults, but given the other issues we're seeing I think it's probably worth
> dropping the LPA2 patches for the moment.
>

Thanks for the analysis Mark.

I agree that this should not be difficult to fix, but given the other
CI problems and identified loose ends, I am not going to object to
dropping this partially or entirely at this point. I'm sure everybody
will be thrilled to go over those 60 patches again after I rebase them
onto v6.7-rc1 :-)