Messages in this thread | | | Date | Mon, 23 Nov 2015 10:38:12 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges |
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* Dan Williams <dan.j.williams@intel.com> wrote:
> On Fri, Nov 20, 2015 at 12:12 PM, Russell King - ARM Linux > <linux@arm.linux.org.uk> wrote: > > On Fri, Nov 20, 2015 at 09:31:33AM -0800, Dan Williams wrote: > >> This effectively promotes IORESOURCE_BUSY to IORESOURCE_EXCLUSIVE > >> semantics by default. If userspace really believes it is safe to access > >> the memory region it can also perform the extra step of disabling an > >> active driver. This protects device address ranges with read side > >> effects and otherwise directs userspace to use the driver. > > > > I'm happy with this as long as we retain the option to disable this > > new behaviour. > > > > The reason being, when developing a driver, it is _very_ useful to > > be able to poke around in the device's (and system memory) address > > spaces with tools like devmem2 to work out what's going on when > > things go wrong. > > > > To put it another way, I think it's a good idea to disable access to > > these regions on production systems, but for driver development, we > > want to retain the ability to poke around in physical address space > > in any way we so desire. > > > > Sounds ok to me, but I do think it's a good idea to default it to the > same value as STRICT_DEVMEM. Perhaps: > > bool "Filter I/O access to /dev/mem" if EXPERT > default STRICT_DEVMEM
Agreed, STRICT_DEVMEM=y should grandfather in this new (and very sensible) restriction.
Thanks,
Ingo
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