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Shutemov" To: Peter Zijlstra Cc: Dave Hansen , Andy Lutomirski , x86@kernel.org, Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv3 5/8] x86/uaccess: Provide untagged_addr() and remove tags before address check Message-ID: <20220616164854.oyvfpl3tzqj54rd6@black.fi.intel.com> References: <20220610143527.22974-1-kirill.shutemov@linux.intel.com> <20220610143527.22974-6-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655398136; a=rsa-sha256; cv=none; b=pQSfrJo0Y3uyyhsv7s5+YIeNMrdD3/WGtMxCejjUur1Ffp11aJZ30Lcr8L6ChRo0AF25sq +t9hIjAySDrAdDj7+qsF6rGVO8LBpw4WjJrwzB1BGCwu2Lz8Oa12KaNy9F150OvwnXdPQj wFHoccRf+A3Dh2ZpLMiL+1Zuh48FKH0= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=hGOXAl94; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf04.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 192.55.52.88) smtp.mailfrom=kirill.shutemov@linux.intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655398136; 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=E+hUADyS7A1YxlHY7IKJmNZGE5eWubzR/pZENls0C+I=; b=GE40eMrBr7/jcfOYmCEQ0iISmzy/L+56aE2lIYFrLe4XTvPrhCWgsWRVhqfA/agZ1LU0fG 8zzgod/Dq68Jlg/zcRm/OknIbGBMKbBJfdmPj8/c8kod3UFfVmleJRJZ0EFkzv646DX52U /NFivR0mEVOlZqOwt1UQgrJAh/IgJQQ= X-Rspamd-Queue-Id: 833E240082 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=hGOXAl94; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf04.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 192.55.52.88) smtp.mailfrom=kirill.shutemov@linux.intel.com X-Rspamd-Server: rspam06 X-Stat-Signature: qz9nfx99gjkmb75q5m65mzzjggsi4636 X-HE-Tag: 1655398136-540163 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 Thu, Jun 16, 2022 at 12:02:16PM +0200, Peter Zijlstra wrote: > On Fri, Jun 10, 2022 at 05:35:24PM +0300, Kirill A. Shutemov wrote: > > +#ifdef CONFIG_X86_64 > > +/* > > + * Mask out tag bits from the address. > > + * > > + * Magic with the 'sign' allows to untag userspace pointer without any branches > > + * while leaving kernel addresses intact. > > + */ > > +#define untagged_addr(mm, addr) ({ \ > > + u64 __addr = (__force u64)(addr); \ > > + s64 sign = (s64)__addr >> 63; \ > > + __addr ^= sign; \ > > + __addr &= (mm)->context.untag_mask; \ > > + __addr ^= sign; \ > > + (__force __typeof__(addr))__addr; \ > > +}) > > Can't we make that mask a constant and *always* unmask U57 irrespective > of LAM being on? We can do this if we give up on LAM_U48. It would also needlessly relax canonical check. I'm not sure it is a good idea. -- Kirill A. Shutemov