From: Alex Williamson <alex.williamson@redhat.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: iommu@lists.linux-foundation.org, ddutile@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] amd_iommu: Fix leak in free_pagetable()
Date: Thu, 20 Jun 2013 13:46:48 -0600 [thread overview]
Message-ID: <1371757608.30572.18.camel@ul30vt.home> (raw)
In-Reply-To: <20130620192638.GD11309@8bytes.org>
On Thu, 2013-06-20 at 21:26 +0200, Joerg Roedel wrote:
> On Thu, Jun 20, 2013 at 01:08:00PM -0600, Alex Williamson wrote:
> > On Thu, 2013-06-20 at 20:28 +0200, Joerg Roedel wrote:
> > > Hmm, actually a recursive version would make more sense here. But since
> > > recursion is a bad idea in the kernel, how about this approach instead:
> >
> > It's a fixed maximum depth of recursion though, is it really that taboo?
>
> Well, a recursive version would be better here because it has lower icache
> impact than my patch. But the risk is if there is a bug in recursive
> code and it goes on forever it will overwrite random kernel memory, with
> undefined, potentially very bad, results (like data corruption, killed
> filesystems and so on).
>
> So in my opinion it is better to not take that risk whenever possible.
But that's true of a bug in any kernel code. I think the only danger
unique to recursion is using too much stack space, but I doubt that's
really an issue for a tiny function with a fixed depth like this. In
case you didn't notice, I did send a recursive version along with the
flat version, but I stupidly used the same subject for both. It's a
little less code and a tiny bit easier to understand than the macro
version. Up to you though. Thanks,
Alex
> > > The IOMMU pagetables can have up to 3 levels, but the code
> >
> > s/3/6/
>
> Right, thanks.
>
> > Seems like it should do the right thing
>
> Ok, I also gave it some testing (started a vm, assigned and de-assigned
> a device), so it should work as expected.
>
> > Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
>
> Thanks,
>
> Joerg
>
>
next prev parent reply other threads:[~2013-06-20 19:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-18 1:48 [PATCH] amd_iommu: Fix leak in free_pagetable() Alex Williamson
2013-06-18 1:52 ` Alex Williamson
2013-06-20 18:28 ` Joerg Roedel
2013-06-20 19:08 ` Alex Williamson
2013-06-20 19:26 ` Joerg Roedel
2013-06-20 19:46 ` Alex Williamson [this message]
2013-06-20 20:04 ` Joerg Roedel
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