From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753037AbbC0SQr (ORCPT ); Fri, 27 Mar 2015 14:16:47 -0400 Received: from www.sr71.net ([198.145.64.142]:56762 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752249AbbC0SQn (ORCPT ); Fri, 27 Mar 2015 14:16:43 -0400 Message-ID: <55159E89.5090007@sr71.net> Date: Fri, 27 Mar 2015 11:16:41 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Borislav Petkov CC: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, dave.hansen@linux.intel.com Subject: Re: [PATCH 15/17] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps References: <20150326183327.64807530@viggo.jf.intel.com> <20150326183353.A2A5B371@viggo.jf.intel.com> <20150327172914.GE5517@pd.tnic> In-Reply-To: <20150327172914.GE5517@pd.tnic> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/27/2015 10:29 AM, Borislav Petkov wrote: >> > +static int mpx_cmpxchg_bd_entry(struct mm_struct *mm, >> > + unsigned long *actual_old_val_ptr, long __user *bd_entry_addr, >> > + unsigned long expected_old_val, unsigned long new_bd_entry) >> > +{ >> > + int ret; >> > + /* >> > + * user_atomic_cmpxchg_inatomic() actually uses sizeof() >> > + * the pointer thatt we pass to it to figure out how much >> > + * data to cmpxchg. We have to be careful here not to >> > + * pass a pointer to a 64-bit data type when we only want >> > + * a 32-bit copy. >> > + */ >> > + if (is_64bit_mm(mm)) { >> > + ret = user_atomic_cmpxchg_inatomic(actual_old_val_ptr, >> > + bd_entry_addr, expected_old_val, new_bd_entry); >> > + } else { >> > + u32 uninitialized_var(actual_old_val_32); >> > + u32 expected_old_val_32 = expected_old_val; >> > + u32 new_bd_entry_32 = new_bd_entry; >> > + u32 __user *bd_entry_32 = (u32 __user *)bd_entry_addr; >> > + ret = user_atomic_cmpxchg_inatomic(&actual_old_val_32, >> > + bd_entry_32, expected_old_val_32, >> > + new_bd_entry_32); > Hmm, I would've added a user_atomic_cmpxchg_inatomic_size() macro which > calls __user_atomic_cmpxchg_inatomic(). That would have saved creating 'u32 __user *bd_entry_32' so that we could implicitly do sizeof(*bd_entry_32). But, what else does it buy us?