From: Christoph Hellwig <h...@lst.de> Sent: Wednesday, April 9, 2025 3:50 AM > > On Tue, Apr 08, 2025 at 11:36:44AM -0700, mhkelle...@gmail.com wrote: > > From: Michael Kelley <mhkli...@outlook.com> > > > > Export vmf_insert_mixed_mkwrite() for use by fbdev deferred I/O code, > > But they are using this on dma coherent memory, where you can't legally > get at the page. As told last time you need to fix that first before > hacking around that code.
Hmmm. What's the reference to "as told last time"? I don't think I've had this conversation before. For the hyperv_fb driver, the memory in question is allocated with a direct call to alloc_pages(), not via dma_alloc_coherent(). There's no DMA in this scenario. The memory is shared with the Hyper-V host and designated as the memory for the virtual framebuffer device. It is then mapped into user space using the mmap() system call against /dev/fb0. User space writes to the memory are eventually (and I omit the details) picked up by the Hyper-V host and displayed. Is your point that memory dma_alloc_coherent() memory must be treated as a black box, and can't be deconstructed into individual pages? If so, that makes sense to me. But must the same treatment be applied to memory from alloc_pages()? This is where I need some education. > > > which can be built as a module. For consistency with the related function > > vmf_insert_mixed(), export without the GPL qualifier. > > No. All advanced new Linux functionality must be _GPL. Don't try to > sneak around that. No problem. Just trying to be consistent, not sneak around anything. Thanks, Michael
