linux-kernel - Re: [PATCH v9 11/12] x86, mpx: cleanup unused bound tables

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5458F819.2010503@intel.com>
Date:	Tue, 04 Nov 2014 08:00:25 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Ren Qiaowei <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, Linux-MM <linux-mm@...ck.org>,
	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	linux-mips@...ux-mips.org
Subject: Re: [PATCH v9 11/12] x86, mpx: cleanup unused bound tables

On 11/03/2014 01:29 PM, Thomas Gleixner wrote:
> On Mon, 3 Nov 2014, Dave Hansen wrote:

> That's not really true. You can evaluate that information with
> mmap_sem held for read as well. Nothing can change the mappings until
> you drop it. So you could do:
> 
>    down_write(mm->bd_sem);
>    down_read(mm->mmap_sem;
>    evaluate_size_of_shm_to_unmap();
>    clear_bounds_directory_entries();
>    up_read(mm->mmap_sem);
>    do_the_real_shm_unmap();
>    up_write(mm->bd_sem);
> 
> That should still be covered by the above scheme.

Yep, that'll work.  It just means rewriting the shmdt()/mremap() code to
do a "dry run" of sorts.

Do you have any concerns about adding another mutex to these paths?
munmap() isn't as hot of a path as the allocation side, but it does
worry me a bit that we're going to perturb some workloads.  We might
need to find a way to optimize out the bd_sem activity on processes that
never used MPX.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/