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Message-ID: <a2dffeeb-04f0-8042-b39a-b839c4800d6f@suse.com>
Date: Tue, 11 Aug 2020 09:57:55 +0200
From: Jürgen Groß <jgross@...e.com>
To: Peter Zijlstra <peterz@...radead.org>,
Marco Elver <elver@...gle.com>
Cc: Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
fenghua.yu@...el.com, "H. Peter Anvin" <hpa@...or.com>,
LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...hat.com>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Luck, Tony" <tony.luck@...el.com>,
the arch/x86 maintainers <x86@...nel.org>,
yu-cheng.yu@...el.com, sdeep@...are.com,
virtualization@...ts.linux-foundation.org,
kasan-dev <kasan-dev@...glegroups.com>,
syzbot <syzbot+8db9e1ecde74e590a657@...kaller.appspotmail.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*()
helpers
On 11.08.20 09:41, Peter Zijlstra wrote:
> On Fri, Aug 07, 2020 at 05:19:03PM +0200, Marco Elver wrote:
>
>> 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
>
> Yes, this is definitely an issue.
>
> Tracing, we also musn't call into tracing when using raw_local_irq_*().
> Because then we re-intoduce this same issue all over again.
>
> Both halt() and safe_halt() are more paravirt calls, but given we're in
> a KVM paravirt call already, I suppose we can directly use native_*()
> here.
>
> Something like so then... I suppose, but then the Xen variants need TLC
> too.
Just to be sure I understand you correct:
You mean that xen_qlock_kick() and xen_qlock_wait() and all functions
called by those should gain the "notrace" attribute, right?
I am not sure why the kick variants need it, though. IMO those are
called only after the lock has been released, so they should be fine
without notrace.
And again: we shouldn't forget the Hyper-V variants.
Juergen
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