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Shutemov" Cc: Bharata B Rao , ananth.narayan@amd.com, "Kirill A. Shutemov" , Dave Hansen , Andy Lutomirski , x86@kernel.org, Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Alexander Potapenko , Taras Madan , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv8 00/11] Linear Address Masking enabling Message-ID: References: <20220830010104.1282-1-kirill.shutemov@linux.intel.com> <20220904010001.knlcejmw4lg2uzy3@box.shutemov.name> <64519d0b-b696-db47-52c2-303451e10c09@amd.com> <20220905134457.a2f7uluq42frsgwe@box.shutemov.name> <20220905153517.k6ctaqqtkcyu2zmn@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220905153517.k6ctaqqtkcyu2zmn@box.shutemov.name> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662392823; a=rsa-sha256; cv=none; b=PzY42b8lEy9O6QJKiOO5t/K3y1DACVTpY+gNOU5UcEnAMZbU2VrW4uK0uIzaYa/vPETGcI TaehF8HDmcdWX+x4nocYeYs6QmBzqQBsof4Sy5TEP/V5CoH/mnIweyp67uBzKimYyd1Q5I jVw8fkOniFC2JOINY7Adwezj4gChwK0= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b="O/HtuUvV"; spf=none (imf11.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662392823; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=fg+XnDXSnqRCu9Mai3sCVJ/hy6+I8T4qZe1klnldH0E=; b=G3uy94atipjejeezqGAR1Hf9b5FNEiIgEYkBLJssW2wHja+33Y3iLS+Ey+sUG3Pzx7hXBS rPTUXYITS3v4jy5+qhd/ys60DJmYPA78c2a2YnTUxySA3yVD5WM4Kl0goomMkeQ0C6I2ii OXE7HOgcFNeMKzfTN69e8VpCE/yCvL4= X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b="O/HtuUvV"; spf=none (imf11.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none X-Rspamd-Server: rspam09 X-Stat-Signature: a7fjwiaep74wehtkek9eooy4hzx9k3hw X-Rspamd-Queue-Id: 5FF094005B X-HE-Tag: 1662392823-177163 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 05, 2022 at 06:35:17PM +0300, Kirill A. Shutemov wrote: > What about something like this? > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > index 803241dfc473..868d2730884b 100644 > --- a/arch/x86/include/asm/uaccess.h > +++ b/arch/x86/include/asm/uaccess.h > @@ -30,8 +30,10 @@ static inline bool pagefault_disabled(void); > */ > #define untagged_addr(mm, addr) ({ \ > u64 __addr = (__force u64)(addr); \ > - s64 sign = (s64)__addr >> 63; \ > - __addr &= (mm)->context.untag_mask | sign; \ > + if (static_cpu_has(X86_FEATURE_LAM)) { \ > + s64 sign = (s64)__addr >> 63; \ > + __addr &= (mm)->context.untag_mask | sign; \ > + } \ > (__force __typeof__(addr))__addr; \ > }) Well, if you go throught the trouble of adding it, might as well use a regular static branch and only enable it once there's an actual user, no?