On Wed, 2019-02-20 at 19:55 +1100, Michael Ellerman wrote: > kvmhv_p9_guest_entry() implements a fast-path guest entry for Power9 > when guest and host are both running with the Radix MMU. > > Currently in that path we don't save the host AMR (Authority Mask > Register) value, and we always restore 0 on return to the host. That > is OK at the moment because the AMR is not used for storage keys with > the Radix MMU. > > However we plan to start using the AMR on Radix to prevent the kernel > from reading/writing to userspace outside of copy_to/from_user(). In > order to make that work we need to save/restore the AMR value. > > We only restore the value if it is different from the guest value, > which is already in the register when we exit to the host. This > should > mean we rarely need to actually restore the value when running a > modern Linux as a guest, because it will be using the same value as > us. > > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Tested-by: Russell Currey <ruscur@xxxxxxxxxx>
