After a few more tests: I still get the same PAGE_NOT_PRESENT errors, as well as a subsequent NULL pointer kernel oops. This occurs both with the new Ubuntu package and with a manually-compiled upstream libdrm. So the mesa/libdrm update does not solve this bug.
After thinking about this, this problem can't be solely a user-space issue; user space should not be able to trigger this kind of kernel oops. Plus, Ben Gamari was already able to bisect this within the kernel. So at least some part of this is related to the kernel-space nouveau component.
After a few more tests: I still get the same PAGE_NOT_PRESENT errors, as well as a subsequent NULL pointer kernel oops. This occurs both with the new Ubuntu package and with a manually-compiled upstream libdrm. So the mesa/libdrm update does not solve this bug.
After thinking about this, this problem can't be solely a user-space issue; user space should not be able to trigger this kind of kernel oops. Plus, Ben Gamari was already able to bisect this within the kernel. So at least some part of this is related to the kernel-space nouveau component.