From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f182.google.com (mail-wi0-f182.google.com [209.85.212.182]) by kanga.kvack.org (Postfix) with ESMTP id 4EA3E6B00DA for ; Thu, 13 Nov 2014 09:29:38 -0500 (EST) Received: by mail-wi0-f182.google.com with SMTP id h11so398707wiw.3 for ; Thu, 13 Nov 2014 06:29:37 -0800 (PST) Received: from Galois.linutronix.de (Galois.linutronix.de. [2001:470:1f0b:db:abcd:42:0:1]) by mx.google.com with ESMTPS id ci8si32533217wib.29.2014.11.13.06.29.37 for (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Thu, 13 Nov 2014 06:29:37 -0800 (PST) Date: Thu, 13 Nov 2014 15:29:26 +0100 (CET) From: Thomas Gleixner Subject: Re: [PATCH 09/11] x86, mpx: on-demand kernel allocation of bounds tables In-Reply-To: <20141112170510.3D07BA53@viggo.jf.intel.com> Message-ID: References: <20141112170443.B4BD0899@viggo.jf.intel.com> <20141112170510.3D07BA53@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: hpa@zytor.com, mingo@redhat.com, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@linux-mips.org, qiaowei.ren@intel.com, dave.hansen@linux.intel.com On Wed, 12 Nov 2014, Dave Hansen wrote: > > From: Dave Hansen > > Thomas, I know you're not a huge fan of using mm->mmap_sem for serializing > this stuff. But, now that we are not adding an additional lock a la > mm->bd_sem, I can't quite justify adding another lock and trying to > reconcile the interactions and ording with mmap_sem. > > We are only adding two spots where we acquire mmap_sem and did not. All of > the other "use" is in places where it is held already. Those two points > of new use are *tiny* and can easily be replaced in the future. I'm fine with that as long as we dont have the "drop, reacquire, handle races of all sorts" dance. > +static inline void arch_bprm_mm_init(struct mm_struct *mm, > + struct vm_area_struct *vma) > +{ > +#ifdef CONFIG_X86_INTEL_MPX > + mm->bd_addr = MPX_INVALID_BOUNDS_DIR; > +#endif > +} > + I'd rather have in mpx.h static inline void mpx_mm_init(struct mm_struct *mm) { #ifdef CONFIG_X86_INTEL_MPX mm->bd_addr = MPX_INVALID_BOUNDS_DIR; #endif } and make this static inline void arch_bprm_mm_init(struct mm_struct *mm, struct vm_area_struct *vma) { mpx_mm_init(mm); } So this #ifdef can be replaced > +++ b/arch/x86/kernel/setup.c 2014-11-12 08:49:26.494916477 -0800 > @@ -959,6 +959,13 @@ void __init setup_arch(char **cmdline_p) > init_mm.end_code = (unsigned long) _etext; > init_mm.end_data = (unsigned long) _edata; > init_mm.brk = _brk_end; > +#ifdef CONFIG_X86_INTEL_MPX > + /* > + * NULL is theoretically a valid place to put the bounds > + * directory, so point this at an invalid address. > + */ > + init_mm.bd_addr = MPX_INVALID_BOUNDS_DIR; > +#endif with mpx_mm_init(&init_mm); > +dotraplinkage void do_bounds(struct pt_regs *regs, long error_code) > +{ > + enum ctx_state prev_state; > + struct bndcsr *bndcsr; > + struct xsave_struct *xsave_buf; > + struct task_struct *tsk = current; > + siginfo_t *info; > + > + prev_state = exception_enter(); > + if (notify_die(DIE_TRAP, "bounds", regs, error_code, > + X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP) > + goto exit; > + conditional_sti(regs); > + > + if (!user_mode(regs)) > + die("bounds", regs, error_code); > + > + if (!cpu_feature_enabled(X86_FEATURE_MPX)) { > + /* The exception is not from Intel MPX */ > + goto exit_trap; > + } > + > + fpu_save_init(&tsk->thread.fpu); That lacks a comment why we need to do an xsave here. > + xsave_buf = &(tsk->thread.fpu.state->xsave); > + bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR); > + if (!bndcsr) > + goto exit_trap; ... > +exit: > + exception_exit(prev_state); And this lacks a: return; Otherwise you can avoid the whole exercise above and just jump to exit_trap :) > +exit_trap: > + /* > + * This path out is for all the cases where we could not > + * handle the exception in some way (like allocating a > + * table or telling userspace about it. We will also end > + * up here if the kernel has MPX turned off at compile > + * time.. > + */ > + do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL); > + exception_exit(prev_state); > +} > +int mpx_handle_bd_fault(struct xsave_struct *xsave_buf) > +{ > + int ret = 0; > + /* > + * Userspace never asked us to manage the bounds tables, > + * so refuse to help. > + */ > + if (!kernel_managing_mpx_tables(current->mm)) { > + ret = -EINVAL; > + goto out; > + } > + > + ret = do_mpx_bt_fault(xsave_buf); > + if (ret) { > + force_sig(SIGSEGV, current); > + /* > + * The force_sig() is essentially "handling" this > + * exception. Return 0 so that the traps.c code > + * does not take any further action. > + */ > + ret = 0; > + } > +out: > + return ret; Wee. That's convoluted. if (!kernel_managing_mpx_tables(current->mm)) return -EINVAL; if (do_mpx_bt_fault(xsave_buf)) { /* Add comment */ force_sig(SIGSEGV, current); } return 0; Does the same thing in a readable form :) Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org