Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*()
 helpers
To:     Peter Zijlstra <peterz@infradead.org>,
        Marco Elver <elver@google.com>
Cc:     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>,
        Wei Liu <wei.liu@kernel.org>
References: <20200806131702.GA3029162@elver.google.com>
 <CANpmjNNqt8YrCad4WqgCoXvH47pRXtSLpnTKhD8W8+UpoYJ+jQ@mail.gmail.com>
 <CANpmjNO860SHpNve+vaoAOgarU1SWy8o--tUWCqNhn82OLCiew@mail.gmail.com>
 <fe2bfa7f-132f-7581-a967-d01d58be1588@suse.com>
 <20200807095032.GA3528289@elver.google.com>
 <16671cf3-3885-eb06-79ff-4cbfaeeaea79@suse.com>
 <20200807113838.GA3547125@elver.google.com>
 <e5bf3e6a-efff-7170-5ee6-1798008393a2@suse.com>
 <CANpmjNPau_DEYadey9OL+iFZKEaUTqnFnyFs1dU12o00mg7ofA@mail.gmail.com>
 <20200807151903.GA1263469@elver.google.com>
 <20200811074127.GR3982@worktop.programming.kicks-ass.net>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <a2dffeeb-04f0-8042-b39a-b839c4800d6f@suse.com>
Date:   Tue, 11 Aug 2020 09:57:55 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200811074127.GR3982@worktop.programming.kicks-ass.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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