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Message-ID: <20181221182515.GF10600@bombadil.infradead.org>
Date: Fri, 21 Dec 2018 10:25:16 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Igor Stoppa <igor.stoppa@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>,
Peter Zijlstra <peterz@...radead.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
igor.stoppa@...wei.com, Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>,
Ahmed Soliman <ahmedsoliman@...a.vt.edu>,
linux-integrity@...r.kernel.org,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/12] x86_64: memset_user()
On Fri, Dec 21, 2018 at 08:14:12PM +0200, Igor Stoppa wrote:
> +unsigned long __memset_user(void __user *addr, int c, unsigned long size)
> +{
> + long __d0;
> + unsigned long pattern = 0;
> + int i;
> +
> + for (i = 0; i < 8; i++)
> + pattern = (pattern << 8) | (0xFF & c);
That's inefficient.
pattern = (unsigned char)c;
pattern |= pattern << 8;
pattern |= pattern << 16;
pattern |= pattern << 32;
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