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.william...@redhat.com> > > Thanks, > > Joerg > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
