Messages in this thread | | | Date | Thu, 7 Nov 2019 11:27:56 +0100 | From | Willy Tarreau <> | Subject | Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further |
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On Thu, Nov 07, 2019 at 02:19:19AM -0800, hpa@zytor.com wrote: > >Changing ioperm(single port, port range) to be ioperm(all) is going to > >break a bunch of test cases which actually check whether the permission > >is restricted to a single I/O port or the requested port range. > > > >Thanks, > > > > tglx > > This seems very undesirable... as much as we might wish otherwise, the port > bitmap is the equivalent to the MMU, and there are definitely users doing > direct device I/O out there.
Doing these, sure, but doing these while ranges are really checked ? I mean, the MMU grants you access to the pages you were assigned. Here with the I/O bitmap you just have to ask for access to port X and you get it. I could understand the benefit if we had EBUSY in return but that's not the case, you can actually request access to a port range another device driver or process is currently using, and mess up with what it does even by accident. I remember streaming 1-bit music in userland from the LED of my floppy drive in the late-90s, it used to cause some trouble to the floppy driver when using mtools in parallel :-)
Willy
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