queue-5.10/x86-mmio-disable-kvm-mitigation-when-x86_feature_clear_cpu_buf-is-set.patch

   1 From stable+bounces-27549-greg=kroah.com@vger.kernel.org Tue Mar 12 23:41:17 2024
   2 From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
   3 Date: Tue, 12 Mar 2024 15:41:07 -0700
   4 Subject: x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set
   5 To: stable@vger.kernel.org
   6 Cc: Dave Hansen <dave.hansen@linux.intel.com>
   7 Message-ID: <20240312-delay-verw-backport-5-10-y-v2-8-ad081ccd89ca@linux.intel.com>
   8 Content-Disposition: inline
   9
  10 From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
  11
  12 commit e95df4ec0c0c9791941f112db699fae794b9862a upstream.
  13
  14 Currently MMIO Stale Data mitigation for CPUs not affected by MDS/TAA is
  15 to only deploy VERW at VMentry by enabling mmio_stale_data_clear static
  16 branch. No mitigation is needed for kernel->user transitions. If such
  17 CPUs are also affected by RFDS, its mitigation may set
  18 X86_FEATURE_CLEAR_CPU_BUF to deploy VERW at kernel->user and VMentry.
  19 This could result in duplicate VERW at VMentry.
  20
  21 Fix this by disabling mmio_stale_data_clear static branch when
  22 X86_FEATURE_CLEAR_CPU_BUF is enabled.
  23
  24 Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
  25 Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
  26 Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  28 ---
  29  arch/x86/kernel/cpu/bugs.c |   14 ++++++++++++--
  30  1 file changed, 12 insertions(+), 2 deletions(-)
  31
  32 --- a/arch/x86/kernel/cpu/bugs.c
  33 +++ b/arch/x86/kernel/cpu/bugs.c
  34 @@ -419,6 +419,13 @@ static void __init mmio_select_mitigatio
  35         if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
  36                                               boot_cpu_has(X86_FEATURE_RTM)))
  37                 setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
  38 +
  39 +       /*
  40 +        * X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
  41 +        * mitigations, disable KVM-only mitigation in that case.
  42 +        */
  43 +       if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
  44 +               static_branch_disable(&mmio_stale_data_clear);
  45         else
  46                 static_branch_enable(&mmio_stale_data_clear);
  47
  48 @@ -495,8 +502,11 @@ static void __init md_clear_update_mitig
  49                 taa_mitigation = TAA_MITIGATION_VERW;
  50                 taa_select_mitigation();
  51         }
  52 -       if (mmio_mitigation == MMIO_MITIGATION_OFF &&
  53 -           boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
  54 +       /*
  55 +        * MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
  56 +        * gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
  57 +        */
  58 +       if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
  59                 mmio_mitigation = MMIO_MITIGATION_VERW;
  60                 mmio_select_mitigation();
  61         }