git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From e910a53fb4f20aa012e46371ffb4c32c8da259b4 Mon Sep 17 00:00:00 2001
   2 From: Maxim Levitsky <mlevitsk@redhat.com>
   3 Date: Wed, 23 Feb 2022 13:56:49 +0200
   4 Subject: KVM: x86: nSVM: disallow userspace setting of MSR_AMD64_TSC_RATIO to non default value when tsc scaling disabled
   5
   6 From: Maxim Levitsky <mlevitsk@redhat.com>
   7
   8 commit e910a53fb4f20aa012e46371ffb4c32c8da259b4 upstream.
   9
  10 If nested tsc scaling is disabled, MSR_AMD64_TSC_RATIO should
  11 never have non default value.
  12
  13 Due to way nested tsc scaling support was implmented in qemu,
  14 it would set this msr to 0 when nested tsc scaling was disabled.
  15 Ignore that value for now, as it causes no harm.
  16
  17 Fixes: 5228eb96a487 ("KVM: x86: nSVM: implement nested TSC scaling")
  18 Cc: stable@vger.kernel.org
  19
  20 Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
  21 Message-Id: <20220223115649.319134-1-mlevitsk@redhat.com>
  22 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  23 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  24 ---
  25  arch/x86/kvm/svm/svm.c |   19 +++++++++++++++++--
  26  1 file changed, 17 insertions(+), 2 deletions(-)
  27
  28 --- a/arch/x86/kvm/svm/svm.c
  29 +++ b/arch/x86/kvm/svm/svm.c
  30 @@ -2903,8 +2903,23 @@ static int svm_set_msr(struct kvm_vcpu *
  31         u64 data = msr->data;
  32         switch (ecx) {
  33         case MSR_AMD64_TSC_RATIO:
  34 -               if (!msr->host_initiated && !svm->tsc_scaling_enabled)
  35 -                       return 1;
  36 +
  37 +               if (!svm->tsc_scaling_enabled) {
  38 +
  39 +                       if (!msr->host_initiated)
  40 +                               return 1;
  41 +                       /*
  42 +                        * In case TSC scaling is not enabled, always
  43 +                        * leave this MSR at the default value.
  44 +                        *
  45 +                        * Due to bug in qemu 6.2.0, it would try to set
  46 +                        * this msr to 0 if tsc scaling is not enabled.
  47 +                        * Ignore this value as well.
  48 +                        */
  49 +                       if (data != 0 && data != svm->tsc_ratio_msr)
  50 +                               return 1;
  51 +                       break;
  52 +               }
  53
  54                 if (data & TSC_RATIO_RSVD)
  55                         return 1;