On Tue, Feb 02, 2021 at 12:44:44AM -0800, Suren Baghdasaryan wrote: > On Mon, Feb 1, 2021 at 11:03 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > IMHO the > > > > BUG_ON(vma->vm_flags & VM_PFNMAP); > > > > in vm_insert_page should just become a WARN_ON_ONCE with an error > > return, and then we just need to gradually fix up the callers that > > trigger it instead of coming up with workarounds like this. > > For the existing vm_insert_page users this should be fine since > BUG_ON() guarantees that none of them sets VM_PFNMAP. Even for them WARN_ON_ONCE plus an actual error return is a way better assert that is much developer friendly. > However, for the > system_heap_mmap I have one concern. When vm_insert_page returns an > error due to VM_PFNMAP flag, the whole mmap operation should fail > (system_heap_mmap returning an error leading to dma_buf_mmap failure). > Could there be cases when a heap user (DRM driver for example) would > be expected to work with a heap which requires VM_PFNMAP and at the > same time with another heap which requires !VM_PFNMAP? IOW, this > introduces a dependency between the heap and its > user. The user would have to know expectations of the heap it uses and > can't work with another heap that has the opposite expectation. This > usecase is purely theoretical and maybe I should not worry about it > for now? If such a case ever arises we can look into it.
