On Thu, Mar 21, 2013 at 12:41:35PM -0600, Jason Gunthorpe wrote: > On Thu, Mar 21, 2013 at 08:16:33PM +0200, Michael S. Tsirkin wrote: > > > This is the one I find redundant. Since the write will be done by > > the adaptor under direct control by the application, why does it > > make sense to declare this beforehand? If you don't want to allow > > local write access to memory, just do not post any receive WRs with > > this address. If you posted and regret it, reset the QP to cancel. > > This is to support your COW scenario - the app declares before hand to > the kernel that it will write to the memory and the kernel ensures > pages are dedicated to the app at registration time. Or the app says > it will only read and the kernel could leave them shared.
Someone here is confused. LOCAL_WRITE/absence of it does not address COW, it breaks COW anyway. Are you now saying we should change rdma so without LOCAL_WRITE it will not break COW? > The adaptor enforces the access control to prevent a naughty app from > writing to shared memory - think about mmap'ing libc.so and then using > RDMA to write to the shared pages. It is necessary to ensure that is > impossible. > > Jason That's why it's redundant: we can't trust an application to tell us 'this page is writeable', we must get this info from kernel. And so there's apparently no need for application to tell adaptor about LOCAL_WRITE. -- MST -- 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/
