queue-4.4/powerpc-fsl-emulate-sprn_bucsr-register.patch

   1 From foo@baz Tue 30 Apr 2019 12:38:50 PM CEST
   2 From: Diana Craciun <diana.craciun@nxp.com>
   3 Date: Mon, 29 Apr 2019 18:49:03 +0300
   4 Subject: powerpc/fsl: Emulate SPRN_BUCSR register
   5 To: stable@vger.kernel.org, gregkh@linuxfoundation.org
   6 Cc: linuxppc-dev@ozlabs.org, mpe@ellerman.id.au, Diana Craciun <diana.craciun@nxp.com>
   7 Message-ID: <1556552948-24957-4-git-send-email-diana.craciun@nxp.com>
   8
   9 From: Diana Craciun <diana.craciun@nxp.com>
  10
  11 commit 98518c4d8728656db349f875fcbbc7c126d4c973 upstream.
  12
  13 In order to flush the branch predictor the guest kernel performs
  14 writes to the BUCSR register which is hypervisor privilleged. However,
  15 the branch predictor is flushed at each KVM entry, so the branch
  16 predictor has been already flushed, so just return as soon as possible
  17 to guest.
  18
  19 Signed-off-by: Diana Craciun <diana.craciun@nxp.com>
  20 [mpe: Tweak comment formatting]
  21 Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
  22 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  23 ---
  24  arch/powerpc/kvm/e500_emulate.c |    7 +++++++
  25  1 file changed, 7 insertions(+)
  26
  27 --- a/arch/powerpc/kvm/e500_emulate.c
  28 +++ b/arch/powerpc/kvm/e500_emulate.c
  29 @@ -277,6 +277,13 @@ int kvmppc_core_emulate_mtspr_e500(struc
  30                 vcpu->arch.pwrmgtcr0 = spr_val;
  31                 break;
  32
  33 +       case SPRN_BUCSR:
  34 +               /*
  35 +                * If we are here, it means that we have already flushed the
  36 +                * branch predictor, so just return to guest.
  37 +                */
  38 +               break;
  39 +
  40         /* extra exceptions */
  41  #ifdef CONFIG_SPE_POSSIBLE
  42         case SPRN_IVOR32: