patches/kernel/0032-KVM-SVM-fix-tsc-scaling-cache-logic.patch

   1 From 955c2b4d64593baecc87c64d1354cd5786975bd9 Mon Sep 17 00:00:00 2001
   2 From: Maxim Levitsky <mlevitsk@redhat.com>
   3 Date: Mon, 6 Jun 2022 21:11:49 +0300
   4 Subject: [PATCH] KVM: SVM: fix tsc scaling cache logic
   5
   6 SVM uses a per-cpu variable to cache the current value of the
   7 tsc scaling multiplier msr on each cpu.
   8
   9 Commit 1ab9287add5e2
  10 ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
  11 broke this caching logic.
  12
  13 Refactor the code so that all TSC scaling multiplier writes go through
  14 a single function which checks and updates the cache.
  15
  16 This fixes the following scenario:
  17
  18 1. A CPU runs a guest with some tsc scaling ratio.
  19
  20 2. New guest with different tsc scaling ratio starts on this CPU
  21    and terminates almost immediately.
  22
  23    This ensures that the short running guest had set the tsc scaling ratio just
  24    once when it was set via KVM_SET_TSC_KHZ. Due to the bug,
  25    the per-cpu cache is not updated.
  26
  27 3. The original guest continues to run, it doesn't restore the msr
  28    value back to its own value, because the cache matches,
  29    and thus continues to run with a wrong tsc scaling ratio.
  30
  31 Fixes: 1ab9287add5e2 ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
  32 Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
  33 Message-Id: <20220606181149.103072-1-mlevitsk@redhat.com>
  34 Cc: stable@vger.kernel.org
  35 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  36 [FE: backport, mainly dropped parts for the not yet present
  37      5228eb96a487 ("KVM: x86: nSVM: implement nested TSC scaling")]
  38 Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
  39 ---
  40  arch/x86/kvm/svm/svm.c | 30 +++++++++++++++++++-----------
  41  1 file changed, 19 insertions(+), 11 deletions(-)
  42
  43 diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
  44 index 938b9b24f0ee..ea87d06bdaba 100644
  45 --- a/arch/x86/kvm/svm/svm.c
  46 +++ b/arch/x86/kvm/svm/svm.c
  47 @@ -468,11 +468,24 @@ static int has_svm(void)
  48         return 1;
  49  }
  50
  51 +void __svm_write_tsc_multiplier(u64 multiplier)
  52 +{
  53 +       preempt_disable();
  54 +
  55 +       if (multiplier == __this_cpu_read(current_tsc_ratio))
  56 +               goto out;
  57 +
  58 +       wrmsrl(MSR_AMD64_TSC_RATIO, multiplier);
  59 +       __this_cpu_write(current_tsc_ratio, multiplier);
  60 +out:
  61 +       preempt_enable();
  62 +}
  63 +
  64  static void svm_hardware_disable(void)
  65  {
  66         /* Make sure we clean up behind us */
  67         if (static_cpu_has(X86_FEATURE_TSCRATEMSR))
  68 -               wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
  69 +               __svm_write_tsc_multiplier(TSC_RATIO_DEFAULT);
  70
  71         cpu_svm_disable();
  72
  73 @@ -514,8 +527,7 @@ static int svm_hardware_enable(void)
  74         wrmsrl(MSR_VM_HSAVE_PA, __sme_page_pa(sd->save_area));
  75
  76         if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
  77 -               wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
  78 -               __this_cpu_write(current_tsc_ratio, TSC_RATIO_DEFAULT);
  79 +               __svm_write_tsc_multiplier(TSC_RATIO_DEFAULT);
  80         }
  81
  82
  83 @@ -1128,9 +1140,10 @@ static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
  84
  85  static void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier)
  86  {
  87 -       wrmsrl(MSR_AMD64_TSC_RATIO, multiplier);
  88 +       __svm_write_tsc_multiplier(multiplier);
  89  }
  90
  91 +
  92  /* Evaluate instruction intercepts that depend on guest CPUID features. */
  93  static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu,
  94                                               struct vcpu_svm *svm)
  95 @@ -1453,13 +1466,8 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
  96                 vmsave(__sme_page_pa(sd->save_area));
  97         }
  98
  99 -       if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
 100 -               u64 tsc_ratio = vcpu->arch.tsc_scaling_ratio;
 101 -               if (tsc_ratio != __this_cpu_read(current_tsc_ratio)) {
 102 -                       __this_cpu_write(current_tsc_ratio, tsc_ratio);
 103 -                       wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio);
 104 -               }
 105 -       }
 106 +       if (static_cpu_has(X86_FEATURE_TSCRATEMSR))
 107 +               __svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
 108
 109         if (likely(tsc_aux_uret_slot >= 0))
 110                 kvm_set_user_return_msr(tsc_aux_uret_slot, svm->tsc_aux, -1ull);
 111 --
 112 2.30.2
 113