Re: [GIT PULL] First batch of KVM changes for 4.1

From: Andy Lutomirski <luto@amacapital.net>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Gleb Natapov <gleb@kernel.org>, kvm list <kvm@vger.kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Andrew Lutomirski <luto@kernel.org>
Subject: Re: [GIT PULL] First batch of KVM changes for 4.1
Date: Mon, 20 Apr 2015 13:27:58 -0700	[thread overview]
Message-ID: <CALCETrW15jX9eh3fqJNzoeD6yveov6rr9NkOLqCe6fJCK_LXoA@mail.gmail.com> (raw)
In-Reply-To: <55353058.2000008@redhat.com>

On Mon, Apr 20, 2015 at 9:59 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 17/04/2015 22:18, Marcelo Tosatti wrote:
>> The bug which this is fixing is very rare, have no memory of a report.
>>
>> In fact, its even difficult to create a synthetic reproducer.
>
> But then why was the task migration notifier even in Jeremy's original
> code for Xen?  Was it supposed to work even on non-synchronized TSC?
>
> If that's the case, then it could be reverted indeed; but then why did
> you commit this patch to 4.1?  Did you think of something that would
> cause the seqcount-like protocol to fail, and that turned out not to be
> the case later?  I was only following the mailing list sparsely in March.

I don't think anyone ever tried that hard to test this stuff.  There
was an infinte loop that Firefox was triggering as a KVM guest
somewhat reliably until a couple months ago in the same vdso code.  :(

--Andy