On Tue, Feb 2, 2021 at 12:51 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > 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. Agree. > > > 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. Sounds good. I'll prepare a new patch and will post it later today. Thanks!
