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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Borislav Petkov <bp@alien8.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Chang S. Bae" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [patch 09/31] x86/fpu: Do not inherit FPU context for CLONE_THREAD
In-Reply-To: <YWWzgO9Vn6XlNsLP@zn.tnic>
References: <20211011215813.558681373@linutronix.de>
 <20211011223610.828296394@linutronix.de> <YWWzgO9Vn6XlNsLP@zn.tnic>
Date:   Tue, 12 Oct 2021 20:52:55 +0200
Message-ID: <87tuhm9it4.ffs@tglx>
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On Tue, Oct 12 2021 at 18:10, Borislav Petkov wrote:

> On Tue, Oct 12, 2021 at 02:00:11AM +0200, Thomas Gleixner wrote:
>> CLONE_THREAD does not have the guarantee of a true fork to inherit all
>> state. Especially the FPU state is meaningless for CLONE_THREAD.
>> 
>> Just wipe out the minimal required state so restore on return to user space
>> let's the thread start with a clean FPU.
>
> This sentence reads weird, needs massaging.

The patch is wrong and needs to be removed. I just double checked
pthread_create() again and it says:

The new thread inherits the calling thread's floating-point environment
(fenv(3))

No idea where I was looking at a few days ago. :(

Thanks,

        tglx