On Tue, Mar 16, 2021 at 04:33:03PM +0100, Daniel Vetter wrote:
> Both kvm (in bd2fae8da794 ("KVM: do not assume PTE is writable after
> follow_pfn")) and vfio (in 07956b6269d3 ("vfio/type1: Use
> follow_pte()")) have lost their callsites of follow_pfn(). All the
> other ones have been switched over to unsafe_follow_pfn because they
> cannot be fixed without breaking userspace api.
>
> Argueably the vfio code is still racy, but that's kinda a bigger
> picture. But since it does leak the pte beyond where it drops the pt
> lock, without anything else like an mmu notifier guaranteeing
> coherence, the problem is at least clearly visible in the vfio code.
> So good enough with me.
>
> I've decided to keep the explanation that after dropping the pt lock
> you must have an mmu notifier if you keep using the pte somehow by
> adjusting it and moving it into the kerneldoc for the new follow_pte()
> function.
>
> Cc: 3...@google.com
> Cc: Jann Horn <ja...@google.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Jason Gunthorpe <j...@nvidia.com>
> Cc: Cornelia Huck <coh...@redhat.com>
> Cc: Peter Xu <pet...@redhat.com>
> Cc: Alex Williamson <alex.william...@redhat.com>
> Cc: linux...@kvack.org
> Cc: linux-arm-ker...@lists.infradead.org
> Cc: linux-samsung-...@vger.kernel.org
> Cc: linux-me...@vger.kernel.org
> Cc: k...@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vet...@intel.com>
> ---
> include/linux/mm.h | 2 --
> mm/memory.c | 26 +++++---------------------
> mm/nommu.c | 13 +------------
> 3 files changed, 6 insertions(+), 35 deletions(-)
I think this is the right thing to do.
Alex is working on fixing VFIO and while kvm is still racy using
follow pte, I think they are working on it too?
Jason
