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Date: Thu, 5 Mar 2015 19:46:13 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@suse.de>,
        Quentin Casasnovas <quentin.casasnovas@oracle.com>,
        Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Pekka Riikonen <priikone@iki.fi>, Rik van Riel <riel@redhat.com>,
        Suresh Siddha <sbsiddha@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>
Subject: Re: Oops with tip/x86/fpu
Message-ID: <20150305184613.GA5432@redhat.com>
References: <54F74F59.5070107@intel.com> <20150304190651.GA5589@redhat.com> <20150304200612.GO3663@pd.tnic> <20150305151442.GA18996@redhat.com> <20150305182203.GA4203@redhat.com> <54F8A1C4.1010504@intel.com>
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On 03/05, Dave Hansen wrote:
>
> On 03/05/2015 10:22 AM, Oleg Nesterov wrote:
> > On 03/05, Oleg Nesterov wrote:
> >> I _think_ that the difference is that eager_fpu_init()->xrstor_state()
> >> was called before apply_alternatives(), so it used XRSTOR.
> >>
> >> Note also that (before this commit) restore_fpu_checking() was almost
> >> never called right after init_fpu(). If use_eager_fpu() == T.
> >>
> >> After this commit the first xrstor_state() uses XRSTORS. And that is
> >> how (I think) 'noxsaves' makes the difference.
> >>
> >>
> >> So. I can be easily wrong, but so far I _think_ that this commit disclosed
> >> another problem. And even if I am wrong and this commit is buggy, we need
> >> to understand why ;)
> >>
> >> I'll try to think about debugging patch, I can't reproduce this problem
> >> on my machine...
> >
> > Dave. could please run the test-case below?
> >
> > Without 'noxsaves', and without my commit.
>
> So you want it tested at 4b2e762e2e5 in tip/x86/fpu?

Yes, or even before, this doesn't really matter I think.

Thanks,

Oleg.