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    SubjectRe: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers
    On Fri, Aug 07, 2020 at 12:35PM +0200, Jürgen Groß wrote:
    > On 07.08.20 11:50, Marco Elver wrote:
    > > On Fri, Aug 07, 2020 at 11:24AM +0200, Jürgen Groß wrote:
    > > > On 07.08.20 11:01, Marco Elver wrote:
    > > > > On Thu, 6 Aug 2020 at 18:06, Marco Elver <elver@google.com> wrote:
    > > > > > On Thu, 6 Aug 2020 at 15:17, Marco Elver <elver@google.com> wrote:
    > > > > > > On Thu, Aug 06, 2020 at 01:32PM +0200, peterz@infradead.org wrote:
    > > > > > > > On Thu, Aug 06, 2020 at 09:47:23AM +0200, Marco Elver wrote:
    > > > > > > > > Testing my hypothesis that raw then nested non-raw
    > > > > > > > > local_irq_save/restore() breaks IRQ state tracking -- see the reproducer
    > > > > > > > > below. This is at least 1 case I can think of that we're bound to hit.
    > > > > > > ...
    > > > > > > >
    > > > > > > > /me goes ponder things...
    > > > > > > >
    > > > > > > > How's something like this then?
    > > > > > > >
    > > > > > > > ---
    > > > > > > > include/linux/sched.h | 3 ---
    > > > > > > > kernel/kcsan/core.c | 62 ++++++++++++++++++++++++++++++++++++---------------
    > > > > > > > 2 files changed, 44 insertions(+), 21 deletions(-)
    > > > > > >
    > > > > > > Thank you! That approach seems to pass syzbot (also with
    > > > > > > CONFIG_PARAVIRT) and kcsan-test tests.
    > > > > > >
    > > > > > > I had to modify it some, so that report.c's use of the restore logic
    > > > > > > works and not mess up the IRQ trace printed on KCSAN reports (with
    > > > > > > CONFIG_KCSAN_VERBOSE).
    > > > > > >
    > > > > > > I still need to fully convince myself all is well now and we don't end
    > > > > > > up with more fixes. :-) If it passes further testing, I'll send it as a
    > > > > > > real patch (I want to add you as Co-developed-by, but would need your
    > > > > > > Signed-off-by for the code you pasted, I think.)
    > > > >
    > > > > I let it run on syzbot through the night, and it's fine without
    > > > > PARAVIRT (see below). I have sent the patch (need your Signed-off-by
    > > > > as it's based on your code, thank you!):
    > > > > https://lkml.kernel.org/r/20200807090031.3506555-1-elver@google.com
    > > > >
    > > > > > With CONFIG_PARAVIRT=y (without the notrace->noinstr patch), I still
    > > > > > get lockdep DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled()), although
    > > > > > it takes longer for syzbot to hit them. But I think that's expected
    > > > > > because we can still get the recursion that I pointed out, and will
    > > > > > need that patch.
    > > > >
    > > > > Never mind, I get these warnings even if I don't turn on KCSAN
    > > > > (CONFIG_KCSAN=n). Something else is going on with PARAVIRT=y that
    > > > > throws off IRQ state tracking. :-/
    > > >
    > > > What are the settings of CONFIG_PARAVIRT_XXL and
    > > > CONFIG_PARAVIRT_SPINLOCKS in this case?
    > >
    > > I attached a config.
    > >
    > > $> grep PARAVIRT .config
    > > CONFIG_PARAVIRT=y
    > > CONFIG_PARAVIRT_XXL=y
    > > # CONFIG_PARAVIRT_DEBUG is not set
    > > CONFIG_PARAVIRT_SPINLOCKS=y
    > > # CONFIG_PARAVIRT_TIME_ACCOUNTING is not set
    > > CONFIG_PARAVIRT_CLOCK=y
    >
    > Anything special I need to do to reproduce the problem? Or would you be
    > willing to do some more rounds with different config settings?

    I can only test it with syzkaller, but that probably doesn't help if you
    don't already have it set up. It can't seem to find a C reproducer.

    I did some more rounds with different configs.

    > I think CONFIG_PARAVIRT_XXL shouldn't matter, but I'm not completely
    > sure about that. CONFIG_PARAVIRT_SPINLOCKS would be my primary suspect.

    Yes, PARAVIRT_XXL doesn't make a different. When disabling
    PARAVIRT_SPINLOCKS, however, the warnings go away.

    Thanks,
    -- Marco

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