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Date:   Fri, 28 Feb 2020 13:51:52 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for
 __fpu__restore_sig()
Message-ID: <20200228125152.nxp6vntmxconc4bj@linutronix.de>
References: <20200121201843.12047-1-yu-cheng.yu@intel.com>
 <20200121201843.12047-9-yu-cheng.yu@intel.com>
 <20200221175859.GL25747@zn.tnic>
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On 2020-02-28 13:17:24 [+0100], Borislav Petkov wrote:
> On Thu, Feb 27, 2020 at 02:52:12PM -0800, Yu-cheng Yu wrote:
> > If TIF_NEED_FPU_LOAD is set, then xstates are already in the xsave buffer. 
> > We can skip saving them again.
> 
> Ok, then pls use test_and_set_thread_flag().

I've been told not to do this while I crafted kernel_fpu_begin() because
this would introduce an atomic operation which we want avoid.

Sebastian