On Saturday, April 29, 2000 at 11:57PM, Ralf Baechle wrote:
>On Thu, Apr 27, 2000 at 08:12:14PM +0200, Kevin D. Kissell wrote:
>> It's a thing that can happen whenever caches are
>> virtually indexed (for speed) but physically tagged
>> (for correctness), and caches get large enough for
>> the algorithm to be wrong once in a while. They can
>> be avoided with a little thought and overhead in the
>> assignment of physical pages to virtual addresses.
>> Gimme a day or so to look at the code, and I'll propose
>> a fix for Linux...
Sadly, I've been handed a more urgent (and more to the
point, paid) assignment, and won't be able to do anything
about this a quickly as I would like. I note that you've posted
a patch, Ralf, so one can hope that it will deal with Florian's
>Apropriate placement of mappings in the address space isn't always possible.
>MAP_FIXED is one example. Aliases in the page cache are harder to handle.
>If one of the page cache mappings is writable then readers may even observe
>stale data or in worst case stale data being written to disk.
mmap() is allowed to fail. I would think that, if someone tries to force an
unsafe mapping, one should give them EINVAL if one doesn't want to deal
with the special case otherwise, or create a copy-on-write clone in a safe
physical page if one wants to be extra-specially nice...