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    SubjectRe: [3.1 patch] x86: default to vsyscall=native
    On Wed, Oct 5, 2011 at 3:30 PM, Adrian Bunk <bunk@stusta.de> wrote:
    > On Thu, Oct 06, 2011 at 12:22:34AM +0200, richard -rw- weinberger wrote:
    >> On Thu, Oct 6, 2011 at 12:13 AM, Andrew Lutomirski <luto@mit.edu> wrote:
    >> > On Mon, Oct 3, 2011 at 10:33 AM, Adrian Bunk <bunk@stusta.de> wrote:
    >> >> On Mon, Oct 03, 2011 at 06:04:53AM -0700, Andrew Lutomirski wrote:
    >> >>> On Mon, Oct 3, 2011 at 2:08 AM, Adrian Bunk <bunk@stusta.de> wrote:
    >> >>> > After upgrading a kernel the existing userspace should just work
    >> >>> > (assuming it did work before ;-) ), but when I upgraded my kernel
    >> >>> > from 3.0.4 to 3.1.0-rc8 a UML instance didn't come up properly.
    >> >>> >
    >> >>> > dmesg said:
    >> >>> >  linux-2.6.30.1[3800] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb9c498 ax:ffffffffff600000 si:0 di:606790
    >> >>> >  linux-2.6.30.1[3856] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb13168 ax:ffffffffff600000 si:0 di:606790
    >> >>> >
    >> >>> > Looking throught the changelog I ended up at commit 3ae36655
    >> >>> > ("x86-64: Rework vsyscall emulation and add vsyscall= parameter").
    >> >>> >
    >> >>> > Linus suggested in https://lkml.org/lkml/2011/8/9/376 to default to
    >> >>> > vsyscall=native.
    >> >>> >
    >> >>> > That sounds reasonable to me, and fixes the problem for me.
    >> >>>
    >> >>> At this point in the -rc cycle, this sounds fine.
    >> >>>
    >> >>> That being said, I'd like to fix it for real for 3.2.  This particular
    >> >>> failure is suspicious -- the "vsyscall fault" message means that
    >> >>> sys_gettimeofday returned EFAULT, which means that the old (3.0 and
    >> >>> before) vgettimeofday should *also* have segfaulted.
    >> >>
    >> >> This 2.6.30.1 UML kernel binary from 2009 worked for me for all host
    >> >> kernels from 2.6.30 to 3.0, and with 3.1.0-rc8 and vsyscall=native
    >> >> it also seems to run nicely.
    >> >>
    >> >> Looking deeper into "a UML instance didn't come up properly",
    >> >> the problem is that it comes up in a strange (readonly) state.
    >> >>
    >> >> There are "Using makefile-style concurrent boot in runlevel S."
    >> >> and "Using makefile-style concurrent boot in runlevel 2." in the
    >> >> logs with a Debian userspace, but no output from the init scripts
    >> >> in these broken bootups (normal messages are in non-broken bootups).
    >> >>
    >> >> Perhaps the two the messages I see in dmesg on the host are from the
    >> >> processes running rcS and rc2 failing early?
    >> >>
    >> >> In a working startup with a Debian userspace, I'm getting during rcS
    >> >>  Setting the system clock.
    >> >>  Cannot access the Hardware Clock via any known method.
    >> >>  Use the --debug option to see the details of our search for an access method.
    >> >>  Unable to set System Clock to: Mon Oct 3 17:01:35 UTC 2011 ... (warning).
    >> >>
    >> >>> We do have a bit
    >> >>> of a bug in that the new code doesn't report si_addr properly, but
    >> >>> that sounds unlikely as a culprit.  Did you try with the offending
    >> >>> commit reverted (i.e. fce8dc0)?  I bet that it also fails there.
    >> >>
    >> >> fce8dc0 is "x86-64: Wire up getcpu syscall", is that really the one you
    >> >> want me to revert?
    >> >>
    >> >>> What's the .config for your UML binary?  I'd like to see if I can
    >> >>> reproduce this.
    >> >>
    >> >> It's attached.
    >> >>
    >> >
    >> > I can't reproduce it.  What distro is running inside the UML instance?
    >>
    >> Same here.
    >> Adrian, is the UML kernel crashing before executing init?
    >
    > As I wrote:
    >  Looking deeper into "a UML instance didn't come up properly",
    >  the problem is that it comes up in a strange (readonly) state.
    >
    > The UML kernel is running happily without crashing, and as I wrote my
    > guess about my problems is:
    >  Perhaps the two the messages I see in dmesg on the host are from the
    >  processes running rcS and rc2 failing early?
    >
    >> We definitely need more information...
    >
    > I gave the information that was requested. plus my observations.
    >
    > What more information exactly do you need from me?

    None :) I just reproduced the problem with Debian Squeeze. Lenny works fine.

    --Andy
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