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Date:   Thu, 12 May 2022 16:35:15 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Laight <David.Laight@aculab.com>
Cc:     "'Kirill A. Shutemov'" <kirill.shutemov@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "H . J . Lu" <hjl.tools@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: Implement Linear Address Masking support
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References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com>
 <20220511022751.65540-2-kirill.shutemov@linux.intel.com>
 <fc54d360620d436f93785ae5e9f8a23f@AcuMS.aculab.com>
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On Thu, May 12, 2022 at 01:01:07PM +0000, David Laight wrote:

> > +static inline int64_t sign_extend64(uint64_t value, int index)
> > +{
> > +    int shift = 63 - index;
> > +    return (int64_t)(value << shift) >> shift;
> > +}
> 
> Shift of signed integers are UB.

The kernel uses -fno-strict-overflow, all the signed UB is gone.