On Wed, Feb 3, 2021 at 2:57 AM Matthew Wilcox willy@infradead.org wrote:
On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with WARN_ON_ONCE and returning an error. This is to ensure users of the vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage and get an indication of an error without panicing the kernel. This will help identifying drivers that need to clear VM_PFNMAP before using dmabuf system heap which is moving to use vm_insert_page.
NACK.
The system may not _panic_, but it is clearly now _broken_. The device doesn't work, and so the system is useless. You haven't really improved anything here. Just bloated the kernel with yet another _ONCE variable that in a normal system will never ever ever be triggered.
Also, what the heck are you doing with your drivers? dma-buf mmap must call dma_buf_mmap(), even for forwarded/redirected mmaps from driver char nodes. If that doesn't work we have some issues with the calling contract for that function, not in vm_insert_page.
Finally why exactly do we need to make this switch for system heap? I've recently looked at gup usage by random drivers, and found a lot of worrying things there. gup on dma-buf is really bad idea in general. -Daniel