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

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Message-ID: <CALCETrW15jX9eh3fqJNzoeD6yveov6rr9NkOLqCe6fJCK_LXoA@mail.gmail.com>
Date:	Mon, 20 Apr 2015 13:27:58 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...nel.org>, kvm list <kvm@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Andrew Lutomirski <luto@...nel.org>
Subject: Re: [GIT PULL] First batch of KVM changes for 4.1

On Mon, Apr 20, 2015 at 9:59 AM, Paolo Bonzini <pbonzini@...hat.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
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