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Date: Fri, 21 Dec 2018 23:05:46 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Igor Stoppa <igor.stoppa@...il.com>,
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 10:25:16AM -0800, Matthew Wilcox wrote:
> 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;
Won't
pattern = 0x0101010101010101 * c;
do the same but faster?
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