From mboxrd@z Thu Jan 1 00:00:00 1970 From: mingo@kernel.org (Ingo Molnar) Date: Mon, 23 Nov 2015 10:38:12 +0100 Subject: [RFC PATCH] restrict /dev/mem to idle io memory ranges In-Reply-To: References: <20151120173133.24259.97028.stgit@dwillia2-desk3.jf.intel.com> <20151120201207.GH8644@n2100.arm.linux.org.uk> Message-ID: <20151123093812.GA28212@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org * Dan Williams wrote: > On Fri, Nov 20, 2015 at 12:12 PM, Russell King - ARM Linux > 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