On 10/01/2015 12:15 PM, Michael S. Tsirkin wrote: > On Thu, Oct 01, 2015 at 11:52:26AM +0300, Avi Kivity wrote: >> I still don't understand your objection to the patch: >> >> >> MSI messages are memory writes so any generic device capable >> of MSI is capable of corrupting kernel memory. >> This means that a bug in userspace will lead to kernel memory corruption >> and crashes. This is something distributions can't support. >> >> >> If a distribution feels it can't support this configuration, it can disable >> the >> uio_pci_generic driver, or refuse to support tainted kernels. If it feels it >> can (and many distributions are starting to support dpdk), then you're just >> denying it the ability to serve its users. > I don't, and can't deny users anything. I merely think upstream should > avoid putting this driver in-tree. By doing this, driver writers will > be pushed to develop solutions that can't crash kernel. > > I pointed out one way to build it, there are sure to be more.
And I pointed out that your solution is unworkable. It's easy to claim that a solution is around the corner, only no one was looking for it, but the reality is that kernel bypass has been a solution for years for high performance users, that it cannot be made safe without an iommu, and that iommus are not available everywhere; and even when they are some users prefer to avoid the performance penalty. > As far as I could see, without this kind of motivation, people do not > even want to try. You are mistaken. The problem is a lot harder than you think. People didn't go and write userspace drivers because they were lazy. They wrote them because there was no other way.
