On Mon, Mar 12, 2018 at 02:28:42PM -0400, Felix Kuehling wrote: > On 2018-03-10 10:01 AM, Christian König wrote: > >> To accomodate those we need to > >> create a "hole" inside the process address space. This patchset have > >> a hack for that (patch 13 HACK FOR HMM AREA), it reserves a range of > >> device file offset so that process can mmap this range with PROT_NONE > >> to create a hole (process must make sure the hole is below 1 << 40). > >> I feel un-easy of doing it this way but maybe it is ok with other > >> folks. > > > > Well we have essentially the same problem with pre gfx9 AMD hardware. > > Felix might have some advise how it was solved for HSA. > > For pre-gfx9 hardware we reserve address space in user mode using a big > mmap PROT_NONE call at application start. Then we manage the address > space in user mode and use MAP_FIXED to map buffers at specific > addresses within the reserved range. > > The big address space reservation causes issues for some debugging tools > (clang-sanitizer was mentioned to me), so with gfx9 we're going to get > rid of this address space reservation. What do you need those mapping for ? What kind of object (pm4 packet command buffer, GPU semaphore | fence, ...) ? Kernel private object ? On nv we need it for the main command buffer ring which we do not want to expose to application. Thus for nv gpu we need kernel to monitor this PROT_NONE region to make sure that i never got unmapped, resize, move ... this is me fearing a rogue userspace that munmap and try to abuse some bug in SVM/GPU driver to abuse object map behind those fix mapping. Cheers, Jérôme
