On Wed, Apr 09, 2025 at 02:10:26PM +0000, Michael Kelley wrote: > Hmmm. What's the reference to "as told last time"? I don't think I've had > this conversation before.
Hmm, there was a conversation about deferred I/O, and I remember the drm folks even defending their abuse of vmalloc_to_page on dma coherent memory against the documentation in the most silly way. Maybe that was a different discussion of the same thing. > > 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. Oh, great. > 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. Yes. > But must the same treatment be applied to memory from > alloc_pages()? This is where I need some education. No, that's just fine.
