+David On Wed, Mar 29, 2023, Paolo Bonzini wrote: > On 3/29/23 18:43, Christian K�nig wrote: > > > > > > > > > 3) other uses of kmap() must switch to MMU-notifier protection. > > > > I would rather suggest to return the page additionally to the pfn from > > hva_to_pfn() when the function was able to grab a reference to it. > > > > When the page is then not available you can't call kmap() on that either. > > > > > > > > If the DRM people are okay with SetPageReserved() as a temporary > > > hack, we can change or remove the WARN in kvm_is_zone_device_page(), > > > since that is what you are referring to in the commit message. > > > > Adding Daniel for additional comments on this, but essentially we have > > changed quite some infrastructure to make sure that everybody uses > > VM_PFNMAP to prevent stuff like this from happening. > > > > I would really prefer a proper solution in KVM instead. > > Hmm... Now that I think about it that would be > > https://lore.kernel.org/kvm/Yc4H+dGfK83BaGpC@xxxxxxxxxx/t/ > > Time to resurrect that work. Ya. I had previously asked David to first eliminated the usage that isn't protected by mmu_notifiers, but after seeing the resulting complexity, I had a change of heart[2]. Can you weigh in on the latter thread, specifically my proposal of using a module param to let the admin opt-in to "unsafe" kmap usage. [1] https://lore.kernel.org/kvm/Ydhq5aHW+JFo15UF@xxxxxxxxxx [2] https://lore.kernel.org/all/ZBEEQtmtNPaEqU1i@xxxxxxxxxx/
