On Sun, Jul 07, 2013 at 07:39:01AM -0700, Guenter Roeck wrote: > On Sun, Jul 07, 2013 at 11:15:11AM +0300, Michael S. Tsirkin wrote: > > On Thu, Jul 04, 2013 at 09:35:00AM -0700, Guenter Roeck wrote: > > > On Thu, Jul 04, 2013 at 05:34:12PM +0300, Michael S. Tsirkin wrote: > > > > On Thu, Jul 04, 2013 at 07:25:23AM -0700, Guenter Roeck wrote: > > > > > On Thu, Jul 04, 2013 at 10:20:23AM +0300, Michael S. Tsirkin wrote: > > > > > > On Thu, Jun 27, 2013 at 10:00:52AM -0700, Guenter Roeck wrote: > > > > > > > On Thu, Jun 27, 2013 at 10:45:01AM +0300, Michael S. Tsirkin wrote: > > > > > > > > On Wed, Jun 26, 2013 at 03:30:23PM -0700, Guenter Roeck wrote: > > > > > > > > > Enable support for MSI interrupts if the device supports it. > > > > > > > > > Since MSI interrupts are edge triggered, it is no longer necessary to > > > > > > > > > disable interrupts in the kernel and re-enable them from user-space. > > > > > > > > > Instead, clearing the interrupt condition in the user space application > > > > > > > > > automatically re-enables the interrupt. > > > > > > > > > > > > > > > > > > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> > > > > > > > > > --- > > > > > > > > > An open question is if we can just do this unconditionally > > > > > > > > > or if there should be some flag to enable it. A module parameter, maybe ? > > > > > > > > > > > > > > > > NACK > > > > > > > > > > > > > > > > UIO is for devices that don't do memory writes. > > > > > > > > Anything that can do writes must be protected by an IOMMU > > > > > > > > and/or have a secure kernel driver, not a UIO stub. > > > > > > > > > > > > > > > > MSI is done by memory writes so if userspace > > > > > > > > controls the device it can trick it to write > > > > > > > > anywhere in memory. > > > > > > > > > > > > > > > Just out of curiosity: Since MSI support is mandatory for all PCIE devices, > > > > > > > isn't that possible anyway, even if MSI is not enabled by the kernel ? > > > > > > > All one would need to do is to enable MSI from user space; after all, > > > > > > > the chip configuration space is writable. > > > > > > > > > > > > > > Thanks, > > > > > > > Guenter > > > > > > > > > > > > If a device has capability to do writes, sure. So don't do this then :) > > > > > > > > > > > Not an option. I need to use MSI. > > > > > > > > > > Not that it matters anymore - turns out it was better writing a specific driver > > > > > for my devices anyway; I needed to be able to disable chip interrupts before > > > > > unloading the driver. But why is it then a reason to NACK this patch ? > > > > > > > > There seem to be two cases - either you can't access the device - > > > > and the uio driver is not useful - or you can, and it's not safe. > > > > In both cases the patch does not seem to bring about anything > > > > except user confusion ... > > > > > > > Sounds like claiming that supporting MSI would cause some kind of confusion. > > > Not sure if I can follow that logic. > > > > > > Actually, it simplifies the user space code a lot. Since MSI interrupts are edge > > > triggered and queued, it is not necessary to disable the interrupts, and all > > > user space has to do is to remove the interrupt reason. Works quite nicely for > > > our devices. > > > > > > As I said, I don't really care too much anymore if this patch is rejected, but > > > the reasons for the rejection are kind of weak. > > > > > > > > Besides, doesn't one have to be root anyway to perform such activities, > > > > > which could then be more easily accomplished by writing into /dev/mem ? > > > > > > > > > > Thanks, > > > > > Guenter > > > > > > > > root might not be able to write into /dev/mem. > > > > > > > I don't really want to try, but at least it is marked rw for root. > > > > > > Guenter > > > > Yes but mechanisms such as selinux can still block it. > > > I hope it can also prevent the use of the the MSI trick on PCIe devices. > After all, the user space mechanisms to write into configuration space > are available for all devices, not just for those with uio drivers. > > Guenter Yes, selinux can also prevent access to sysfs and procfs for any process. -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
