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Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for
 __fpu__restore_sig()
From:   Yu-cheng Yu <yu-cheng.yu@intel.com>
To:     Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Date:   Fri, 28 Feb 2020 08:20:27 -0800
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On Fri, 2020-02-28 at 17:23 +0100, Borislav Petkov wrote:
> On Fri, Feb 28, 2020 at 07:53:38AM -0800, Yu-cheng Yu wrote:
> > Yes, saving only supervisor states is optimal, but doing XSAVES with a
> > partial RFBM changes xcomp_bv.
> 
> ... and that means what exactly in plain english?

When XSAVES writes to an xsave buffer, xsave->header.xcomp_bv is set to
include only saved components, effectively changing the buffer's format.

I will include this in the comments.

Yu-cheng