Hi Gerd, On Fri, Aug 30, 2019 at 4:16 AM Gerd Hoffmann <kra...@redhat.com> wrote: > > Hi, > > > > > - kfree(vbuf->data_buf); > > > > + kvfree(vbuf->data_buf); > > > > > > if (is_vmalloc_addr(vbuf->data_buf)) ... > > > > > > needed here I gues? > > > > > > > kvfree() handles vmalloc/kmalloc/kvmalloc internally by doing that check. > > Ok. > > > - videobuf_vmalloc_to_sg in drivers/media/v4l2-core/videobuf-dma-sg.c, > > assumes contiguous array of scatterlist and that the buffer being converted > > is page aligned > > Well, vmalloc memory _is_ page aligned.
True, but this function gets called for all potential enqueuings (eg resource_create_3d, resource_attach_backing) and I was concerned that some other usage in the future might not have that guarantee. But if that's overly being paranoid, I'm willing to backtrack on that. > sg_alloc_table_from_pages() does alot of what you need, you just need a > small loop around vmalloc_to_page() create a struct page array > beforehand. That feels like an extra allocation when under memory pressure and more work, to not gain much -- there still needs to be a function that iterates through all the pages. But I don't feel super strongly about it and can change it if you think that it will be less maintenance overhead. > Completely different approach: use get_user_pages() and don't copy the > execbuffer at all. This one I'd rather not do unless we can show that the copy is actually a problem. As it stands I expect this to be a fallback instead of the regular case, and if it's not then the VMs need to revisit how long the control queue size is. Right now most execbuffers end up being copied into a single contiguous buffer which results in 3 descriptors of the virtio queue. If vmalloc ends up being used (which is only a fallback because vmemdup_user tries kmalloc first still), then there'll be 66 descriptors for a 256KB buffer. I think that's fine for exceptional cases, but not ideal if it was commonplace. Chia-I suggested that we could have a flag for the ioctl execbuffer indicating that the buffer is BO to solve that, but again I'd prefer to see that it's actually a problem. I'll also be moving the sg table construction out of the critical section and properly accounting for the required number of descriptors before entering it in response to his comments. Thanks, Dave _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
