On Mon, Feb 11, 2019 at 10:40:02PM +0000, Weiny, Ira wrote: > > Many drivers do this, the 'doorbell' is a PCI -> CPU thing of some sort > > My surprise is why does _userspace_ allocate this memory? Well, userspace needs to read the memory, so either userpace allocates it and the kernel GUP's it, or userspace mmap's a kernel page which was DMA mapped. The GUP version lets the doorbells have lower alignment than a PAGE, and thes RDMA drivers hard requires GUP->DMA to function.. So why not use a umem here? It already has to work. > > > This does not seem to be allocating memory regions. Jason, do you > > > want a patch to just convert these calls and consider it legacy code? > > > > It needs to use umem like all the other drivers on this path. > > Otherwise it doesn't get the page pinning logic right > > Not sure what you mean regarding the pinning logic? The RLIMIT_MEMLOCK stuff and so on. > > There is also something else rotten with these longterm callsites, > > they seem to have very different ideas how to handle > > RLIMIT_MEMLOCK. > > > > ie vfio doesn't even touch pinned_vm.. and rdma is applying > > RLIMIT_MEMLOCK to mm->pinned_vm, while vfio is using locked_vm.. No > > idea which is right, but they should be the same, and this pattern should > > probably be in core code someplace. > > Neither do I. But AFAIK pinned_vm is a subset of locked_vm. I thought so.. > So should we be accounting both of the counters? Someone should check :) Since we don't increment locked_vm when we increment pinned_vm and vfio only checke RLIMIT_MEMLOCK against locked_vm one can certainly exceed the limit by mixing and matching RDMA and VFIO pins in the same process. Sure seems like there is a bug somewhere here. Jason
