On Thu, Oct 08, 2015 at 08:01:21PM +0300, Gleb Natapov wrote: > On Thu, Oct 08, 2015 at 07:43:04PM +0300, Michael S. Tsirkin wrote: > > On Thu, Oct 08, 2015 at 04:28:34PM +0300, Gleb Natapov wrote: > > > On Thu, Oct 08, 2015 at 04:20:04PM +0300, Michael S. Tsirkin wrote: > > > > On Thu, Oct 08, 2015 at 03:27:37PM +0300, Gleb Natapov wrote: > > > > > On Thu, Oct 08, 2015 at 03:06:07PM +0300, Michael S. Tsirkin wrote: > > > > > > On Thu, Oct 08, 2015 at 12:44:09PM +0300, Avi Kivity wrote: > > > > > > > > > > > > > > > > > > > > > On 10/08/2015 12:16 PM, Michael S. Tsirkin wrote: > > > > > > > >On Thu, Oct 08, 2015 at 11:46:30AM +0300, Avi Kivity wrote: > > > > > > > >> > > > > > > > >>On 10/08/2015 10:32 AM, Michael S. Tsirkin wrote: > > > > > > > >>>On Thu, Oct 08, 2015 at 08:33:45AM +0300, Avi Kivity wrote: > > > > > > > >>>>It is good practice to defend against root oopsing the > > > > > > > >>>>kernel, but in some > > > > > > > >>>>cases it cannot be achieved. > > > > > > > >>>Absolutely. That's one of the issues with these patches. They > > > > > > > >>>don't even > > > > > > > >>>try where it's absolutely possible. > > > > > > > >>> > > > > > > > >>Are you referring to blocking the maps of the msix BAR areas? > > > > > > > >For example. There are more. I listed some of the issues on the > > > > > > > >mailing > > > > > > > >list, and I might have missed some. VFIO has code to address > > > > > > > >all this, > > > > > > > >people should share code to avoid duplication, or at least read > > > > > > > >it > > > > > > > >to understand the issues. > > > > > > > > > > > > > > All but one of those are unrelated to the patch that adds msix > > > > > > > support. > > > > > > > > > > > > They are related because msix support enables bus mastering. > > > > > > Without it > > > > > > device is passive and can't harm anyone. With it, suddently you > > > > > > need to > > > > > > be very careful with the device to avoid corrupting kernel memory. > > > > > > > > > > > Most (if not all) uio_pci_generic users enable pci bus mastering. The > > > > > fact that they do that without even tainting the kernel like the patch > > > > > does make current situation much worse that with the patch. > > > > > > > > It isn't worse. It's a sane interface. Whoever enables bus mastering > > > > must be careful. If userspace enables bus mastering then userspace > > > > needs to be very careful with the device to avoid corrupting kernel > > > > memory. If kernel does it, it's kernel's responsibility. > > > > > > > Although this definition of sanity sounds strange to me, but lets > > > flow with it for the sake of this email: would it be OK if proposed > > > interface refused to work if bus mastering is not already enabled by > > > userspace? > > > > An interface could be acceptable if there's a fallback where it > > works without BM but slower (e.g. poll pending bits). > > > OK. > > > But not the proposed one. > > > Why? Greg is against ioctl interface so it will be reworked, by besides > that what is wrong with the concept of binding msi-x interrupt to > eventfd?
It's not the binding. Managing msi-x just needs more than the puny 2 ioctls to get # of vectors and set eventfd. It interacts in strange ways with reset, and with PM, and ... > > Really, there's more to making msi-x work with > > userspace drivers than this patch. As I keep telling people, you would > > basically reimplement vfio/pci. Go over it, and see for yourself. > > Almost everything it does is relevant for msi-x. It's just wrong to > > duplicate so much code. > > > The patch is tested and works with msi-x. Restricting access to msi-x > registers that vfio does is not relevant here. It works *for you* with a specific userspace application. I have no idea how you tested it, and what does the userspace in question do. But it seems pretty clear that there are a ton of very reasonable things that one can do with a device and that break when you enable MSI-X. You need to find a way to share that logic with vfio/pci. > -- > Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
