Messages in this thread | | | Date | Fri, 20 Nov 2015 12:26:13 -0800 | Subject | Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges | From | Dan Williams <> |
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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
When this in do we even need IORESOURCE_EXCLUSIVE? It's barely used.
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