Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220610143527.22974-1-kirill.shutemov@linux.intel.com>
 <20220610143527.22974-6-kirill.shutemov@linux.intel.com> <c7e2f8fb44da067e7565d091edeac300977b65ed.camel@intel.com>
 <Yqr4SVMyHRTkc+LN@hirez.programming.kicks-ass.net> <20220616164440.vw7sqnof6grrmnvl@black.fi.intel.com>
 <YqxnMbMhvWO9rEy4@worktop.programming.kicks-ass.net>
In-Reply-To: <YqxnMbMhvWO9rEy4@worktop.programming.kicks-ass.net>
From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Fri, 17 Jun 2022 07:22:57 -0700
Message-ID: <CAMe9rOq_WT-dxS3xthGtagn=aHruHyUJDR_=RDvMi9vX5PCmnA@mail.gmail.com>
Subject: Re: [PATCHv3 5/8] x86/uaccess: Provide untagged_addr() and remove
 tags before address check
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
        "Lutomirski, Andy" <luto@kernel.org>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "kcc@google.com" <kcc@google.com>,
        "andreyknvl@gmail.com" <andreyknvl@gmail.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "dvyukov@google.com" <dvyukov@google.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "ryabinin.a.a@gmail.com" <ryabinin.a.a@gmail.com>,
        "glider@google.com" <glider@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Jun 17, 2022 at 4:36 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Jun 16, 2022 at 07:44:40PM +0300, Kirill A. Shutemov wrote:
> > Any objection against this variant (was posted in the thread):
> >
> >               #define untagged_addr(mm, addr) ({                                      \
> >                       u64 __addr = (__force u64)(addr);                               \
> >                       s64 sign = (s64)__addr >> 63;                                   \
> >                       __addr &= (mm)->context.untag_mask | sign;                      \
> >                       (__force __typeof__(addr))__addr;                               \
> >               })
> >
> > ?
>
> Yeah, I suppose that should work fine.

Won't the sign bit be put at the wrong place?

-- 
H.J.