linux-kernel - Re: [RFC 3/3] SGI Altix cross partition memory (XPMEM)

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]

Date:	Thu, 9 Aug 2007 23:15:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dean Nelson <dcn@....com>
Cc:	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, tony.luck@...el.com, jes@....com
Subject: Re: [RFC 3/3] SGI Altix cross partition memory (XPMEM)

On Thu, 9 Aug 2007 20:14:35 -0500 Dean Nelson <dcn@....com> wrote:

> This patch provides cross partition access to user memory (XPMEM) when
> running multiple partitions on a single SGI Altix.
> 

- Please don't send multiple patches all with the same title.

- Feed the diff through checkpatch.pl, ponder the result.

- Avoid needless casts to and from void* (eg, vm_private_data)

- The test for PF_DUMPCORE in xpmem_fault_handler() is mysterious and
  merits a comment.

- xpmem_fault_handler() is scary.

- xpmem_fault_handler() appears to have imposed a kernel-wide rule that
  when taking multiple mmap_sems, one should take the lowest-addressed one
  first?  If so, that probably wants a mention in that locking comment in
  filemap.c

- xpmem_fault_handler() does atomic_dec(&seg_tg->mm->mm_users).  What
  happens if that was the last reference?

- Has it all been tested with lockdep enabled?  Jugding from all the use
  of SPIN_LOCK_UNLOCKED, it has not.

  Oh, ia64 doesn't implement lockdep.  For this code, that is deeply
  regrettable.

- This code all predates the nopage->fault conversion and won't work in
  current kernels.

- xpmem_attach() does smp_processor_id() in preemptible code.  Lucky that
  ia64 doesn't do preempt?

- Stuff like this:

+	ap_tg = xpmem_tg_ref_by_apid(apid);
+	if (IS_ERR(ap_tg))
+		return PTR_ERR(ap_tg);
+
+	ap = xpmem_ap_ref_by_apid(ap_tg, apid);
+	if (IS_ERR(ap)) {
+		xpmem_tg_deref(ap_tg);
+		return PTR_ERR(ap);
+	}

  is fragile.  It is easy to introduce leaks and locking errors as the
  code evolves.  The code has a lot of these deeply-embedded `return'
  statments preceded by duplicated unwinding.  Kenrel code generally
  prefers to do the `goto out' thing.


- "XPMEM_FLAG_VALIDPTEs"?  Someone's pinky got tired at the end ;)

Attention span expired at 19%, sorry.  It's a large patch.
-
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/