From: Marco Elver <elver@google.com>
To: "Jürgen Groß" <jgross@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
fenghua.yu@intel.com, "H. Peter Anvin" <hpa@zytor.com>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Luck, Tony" <tony.luck@intel.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
yu-cheng.yu@intel.com, sdeep@vmware.com,
virtualization@lists.linux-foundation.org,
kasan-dev <kasan-dev@googlegroups.com>,
syzbot <syzbot+8db9e1ecde74e590a657@syzkaller.appspotmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers
Date: Tue, 11 Aug 2020 09:00:32 +0200 [thread overview]
Message-ID: <CANpmjNM1jASqCFYZpteVrZCa2V2D_DbXaqvoCV_Ac2boYfDXnQ@mail.gmail.com> (raw)
In-Reply-To: <20200807151903.GA1263469@elver.google.com>
On Fri, 7 Aug 2020 at 17:19, Marco Elver <elver@google.com> wrote:
> On Fri, Aug 07, 2020 at 02:08PM +0200, Marco Elver wrote:
> > On Fri, 7 Aug 2020 at 14:04, Jürgen Groß <jgross@suse.com> wrote:
> > >
> > > On 07.08.20 13:38, Marco Elver wrote:
> > > > On Fri, Aug 07, 2020 at 12:35PM +0200, Jürgen Groß wrote:
...
> > > >> 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 for testing!
> > >
> > > I take it you are doing the tests in a KVM guest?
> >
> > Yes, correct.
> >
> > > If so I have a gut feeling that the use of local_irq_save() and
> > > local_irq_restore() in kvm_wait() might be fishy. I might be completely
> > > wrong here, though.
> >
> > Happy to help debug more, although I might need patches or pointers
> > what to play with.
> >
> > > BTW, I think Xen's variant of pv spinlocks is fine (no playing with IRQ
> > > on/off).
> > >
> > > Hyper-V seems to do the same as KVM, and kicking another vcpu could be
> > > problematic as well, as it is just using IPI.
>
> I experimented a bit more, and the below patch seems to solve the
> warnings. However, that was based on your pointer about kvm_wait(), and
> I can't quite tell if it is the right solution.
>
> My hypothesis here is simply that kvm_wait() may be called in a place
> where we get the same case I mentioned to Peter,
>
> raw_local_irq_save(); /* or other IRQs off without tracing */
> ...
> kvm_wait() /* IRQ state tracing gets confused */
> ...
> raw_local_irq_restore();
>
> and therefore, using raw variants in kvm_wait() works. It's also safe
> because it doesn't call any other libraries that would result in corrupt
> IRQ state AFAIK.
Just to follow-up, it'd still be nice to fix this. Suggestions?
I could send the below as a patch, but can only go off my above
hypothesis and the fact that syzbot is happier, so not entirely
convincing.
Thanks,
-- Marco
> ------ >8 ------
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 233c77d056c9..1d412d1466f0 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -797,7 +797,7 @@ static void kvm_wait(u8 *ptr, u8 val)
> if (in_nmi())
> return;
>
> - local_irq_save(flags);
> + raw_local_irq_save(flags);
>
> if (READ_ONCE(*ptr) != val)
> goto out;
> @@ -810,10 +810,10 @@ static void kvm_wait(u8 *ptr, u8 val)
> if (arch_irqs_disabled_flags(flags))
> halt();
> else
> - safe_halt();
> + raw_safe_halt();
>
> out:
> - local_irq_restore(flags);
> + raw_local_irq_restore(flags);
> }
>
> #ifdef CONFIG_X86_32
next prev parent reply other threads:[~2020-08-11 7:01 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-05 7:19 upstream test error: WARNING in __local_bh_enable_ip syzbot
2020-08-05 13:26 ` [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers Marco Elver
2020-08-05 13:42 ` peterz
2020-08-05 13:59 ` Marco Elver
2020-08-05 14:12 ` peterz
2020-08-05 14:17 ` Jürgen Groß
2020-08-05 14:17 ` peterz
2020-08-05 14:36 ` Marco Elver
2020-08-05 17:31 ` Marco Elver
2020-08-06 7:47 ` Marco Elver
2020-08-06 11:32 ` peterz
2020-08-06 13:17 ` Marco Elver
2020-08-06 16:06 ` Marco Elver
2020-08-07 9:01 ` Marco Elver
2020-08-07 9:24 ` Jürgen Groß
2020-08-07 9:50 ` Marco Elver
2020-08-07 10:35 ` Jürgen Groß
2020-08-07 11:38 ` Marco Elver
2020-08-07 12:04 ` Jürgen Groß
2020-08-07 12:08 ` Marco Elver
2020-08-07 15:19 ` Marco Elver
2020-08-11 7:00 ` Marco Elver [this message]
2020-08-11 7:04 ` Jürgen Groß
2020-08-11 7:41 ` Peter Zijlstra
2020-08-11 7:57 ` Jürgen Groß
2020-08-11 8:12 ` Peter Zijlstra
2020-08-11 8:18 ` Jürgen Groß
2020-08-11 8:38 ` Jürgen Groß
2020-08-11 9:20 ` peterz
2020-08-11 9:46 ` peterz
2020-08-11 20:17 ` peterz
2020-08-12 8:06 ` Marco Elver
2020-08-12 8:18 ` peterz
2020-08-12 8:57 ` peterz
2020-08-06 21:02 ` kernel test robot
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