Subject: Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?
To: Andy Lutomirski <luto@amacapital.net>
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Cc: Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>,
        Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Brian Gerst <brgerst@gmail.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <56788478.9050805@linux.intel.com>
Date: Mon, 21 Dec 2015 15:00:08 -0800
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On 12/21/2015 02:52 PM, Andy Lutomirski wrote:
> Perhaps this is silly, but what if the default were changed to deny
> reads and writes for unallocated keys?  Is there a use case that
> breaks?

It's probably a reasonable debugging feature.

But, anything that takes an XSAVE feature out of its "init state" has
the potential to do a bit of harm because it increases the potential
size of writes during XSAVE.  XSAVEOPT will _help_ here, but we probably
don't want to go out of our way to take things out of the init state
when we're unsure of the benefits.
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