Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





On 1/27/2021 12:31 AM, Paolo Bonzini wrote:
On 08/01/21 07:49, Chenyi Qiang wrote:
To avoid breaking the CPUs without bus lock detection, activate the
DR6_BUS_LOCK bit (bit 11) conditionally in DR6_FIXED_1 bits.

The set/clear of DR6_BUS_LOCK is similar to the DR6_RTM in DR6
register. The processor clears DR6_BUS_LOCK when bus lock debug
exception is generated. (For all other #DB the processor sets this bit
to 1.) Software #DB handler should set this bit before returning to the
interrupted task.

For VM exit caused by debug exception, bit 11 of the exit qualification
is set to indicate that a bus lock debug exception condition was
detected. The VMM should emulate the exception by clearing bit 11 of the
guest DR6.

Please rename DR6_INIT to DR6_ACTIVE_LOW, and then a lot of changes become simpler:

-        dr6 |= DR6_BD | DR6_RTM;
+        dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;

dr6 |= DR6_BD | DR6_ACTIVE_LOW;

          ctxt->ops->set_dr(ctxt, 6, dr6);
          return emulate_db(ctxt);
      }
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index cce0143a6f80..3d8a0e30314f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1860,7 +1860,7 @@ static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
      get_debugreg(vcpu->arch.db[2], 2);
      get_debugreg(vcpu->arch.db[3], 3);
      /*
-     * We cannot reset svm->vmcb->save.dr6 to DR6_FIXED_1|DR6_RTM here,
+     * We cannot reset svm->vmcb->save.dr6 to DR6_FIXED_1|DR6_RTM|DR6_BUS_LOCK here,

We cannot reset svm->vmcb->save.dr6 to DR6_ACTIVE_LOW

       * because db_interception might need it.  We can do it before vmentry.
       */
      vcpu->arch.dr6 = svm->vmcb->save.dr6;
@@ -1911,7 +1911,7 @@ static int db_interception(struct vcpu_svm *svm)
      if (!(svm->vcpu.guest_debug &
            (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) &&
          !svm->nmi_singlestep) {
-        u32 payload = (svm->vmcb->save.dr6 ^ DR6_RTM) & ~DR6_FIXED_1;
+        u32 payload = (svm->vmcb->save.dr6 ^ (DR6_RTM|DR6_BUS_LOCK)) & ~DR6_FIXED_1;

u32 payload = svm->vmcb->save.dr6 ^ DR6_ACTIVE_LOW;

          kvm_queue_exception_p(&svm->vcpu, DB_VECTOR, payload);
          return 1;
      }
@@ -3778,7 +3778,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)       if (unlikely(svm->vcpu.arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT))
          svm_set_dr6(svm, vcpu->arch.dr6);
      else
-        svm_set_dr6(svm, DR6_FIXED_1 | DR6_RTM);
+        svm_set_dr6(svm, DR6_FIXED_1 | DR6_RTM | DR6_BUS_LOCK);

svm_set_dr6(svm, DR6_ACTIVE_LOW);

      clgi();
      kvm_load_guest_xsave_state(vcpu);
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index e2f26564a12d..c5d71a9b3729 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -412,7 +412,7 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned long *exit
              if (!has_payload) {
                  payload = vcpu->arch.dr6;
                  payload &= ~(DR6_FIXED_1 | DR6_BT);
-                payload ^= DR6_RTM;
+                payload ^= DR6_RTM | DR6_BUS_LOCK;

payload &= ~DR6_BT;
payload ^= DR6_ACTIVE_LOW;

              }
              *exit_qual = payload;
          } else
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3f7c1fc7a3ce..06de2b9e57f3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -483,19 +483,20 @@ void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu)
           */
          vcpu->arch.dr6 &= ~DR_TRAP_BITS;
          /*
-         * DR6.RTM is set by all #DB exceptions that don't clear it.
+         * DR6.RTM and DR6.BUS_LOCK are set by all #DB exceptions
+         * that don't clear it.
           */
-        vcpu->arch.dr6 |= DR6_RTM;
+        vcpu->arch.dr6 |= DR6_RTM | DR6_BUS_LOCK;
          vcpu->arch.dr6 |= payload;
          /*
-         * Bit 16 should be set in the payload whenever the #DB
-         * exception should clear DR6.RTM. This makes the payload
-         * compatible with the pending debug exceptions under VMX.
-         * Though not currently documented in the SDM, this also
-         * makes the payload compatible with the exit qualification
-         * for #DB exceptions under VMX.
+         * Bit 16/Bit 11 should be set in the payload whenever
+         * the #DB exception should clear DR6.RTM/DR6.BUS_LOCK.
+         * This makes the payload compatible with the pending debug
+         * exceptions under VMX. Though not currently documented in
+         * the SDM, this also makes the payload compatible with the
+         * exit qualification for #DB exceptions under VMX.
           */
-        vcpu->arch.dr6 ^= payload & DR6_RTM;
+        vcpu->arch.dr6 ^= payload & (DR6_RTM | DR6_BUS_LOCK);

vcpu->arch.dr6 &= ~DR_TRAP_BITS;
vcpu->arch.dr6 |= DR6_ACTIVE_LOW;
vcpu->arch.dr6 |= payload;
vcpu->arch.dr6 ^= payload & DR6_ACTIVE_LOW;

(with comments :))

and so on.

Thanks!

Paolo


Will do the changes.

Thanks!
Chenyi

          /*
           * The #DB payload is defined as compatible with the 'pending
@@ -1126,6 +1127,9 @@ static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu)
      if (!guest_cpuid_has(vcpu, X86_FEATURE_RTM))
          fixed |= DR6_RTM;
+
+    if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+        fixed |= DR6_BUS_LOCK;
      return fixed;
  }
@@ -7197,7 +7201,8 @@ static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu)
      struct kvm_run *kvm_run = vcpu->run;
      if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
-        kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1 | DR6_RTM;
+        kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1 | DR6_RTM |
+                      DR6_BUS_LOCK;
          kvm_run->debug.arch.pc = kvm_get_linear_rip(vcpu);
          kvm_run->debug.arch.exception = DB_VECTOR;
          kvm_run->exit_reason = KVM_EXIT_DEBUG;
@@ -7241,7 +7246,8 @@ static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
                         vcpu->arch.eff_db);
          if (dr6 != 0) {
-            kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1 | DR6_RTM;
+            kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1 | DR6_RTM |
+                          DR6_BUS_LOCK;
              kvm_run->debug.arch.pc = eip;
              kvm_run->debug.arch.exception = DB_VECTOR;
              kvm_run->exit_reason = KVM_EXIT_DEBUG;





[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux