Messages in this thread | | | Date | Mon, 18 May 2015 23:55:24 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 17/19] x86, mpx: rewrite unmap code |
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On Fri, 8 May 2015, Dave Hansen wrote: > The MPX code needs to clear out bounds tables for memory which > is no longer in use. We do this when a userspace mapping is > torn down (unmapped). > > There are two modes: > 1. An entire bounds table becomes unused, and can be freed > and its pointer removed from the bounds directory. This > happens either when a large mapping is torn down, or when > a small mapping is torn down and it is the last mapping > "covered" by a bounds table. > 2. Only part of a bounds table becomes unused, in which case > we free the backing memory as if MADV_DONTNEED was called. > > The old code was a spaghetti mess of "edge" bounds tables > where the edges were handled specially, even if we were > unmapping an entire one. Non-edge bounds tables are always > fully unmapped, but share a different code path from the edge > ones. The old code had a bug where it was unmapping too much > memory. I worked on fixing it for two days and gave up. > > I didn't write the original code. I didn't particularly like > it, but it worked, so I left it. After my debug session, I > realized it was undebuggagle *and* buggy, so out it went. > > I also wrote a new unmapping test program which uncovers bugs > pretty nicely.
Very appreciated. This is really readable now.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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