On Mon, Mar 24, 2025, Manali Shukla wrote:
> + if (vmcb02->save.rip && (svm->nested.ctl.bus_lock_rip ==
> vmcb02->save.rip)) {
> + vmcb02->control.bus_lock_counter = 1;
> + svm->bus_lock_rip = svm->nested.ctl.bus_lock_rip;
> + } else {
> + vmcb02->control.bus_lock_counter = 0;
> + }
> + svm->nested.ctl.bus_lock_rip = INVALID_GPA;
> +
> /* Done at vmrun: asid. */
>
> /* Also overwritten later if necessary. */
> @@ -1039,6 +1069,18 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>
> }
>
> + /*
> + * If bus_lock_counter is nonzero and the guest has not moved past the
> + * guilty instruction, save bus_lock_rip in svm_nested_state. This will
> + * help determine at nested VMRUN whether to stash vmcb02's counter or
> + * reset it to '0'.
> + */
> + if (vmcb02->control.bus_lock_counter &&
> + svm->bus_lock_rip == vmcb02->save.rip)
> + svm->nested.ctl.bus_lock_rip = svm->bus_lock_rip;
> + else
> + svm->nested.ctl.bus_lock_rip = INVALID_GPA;
> +
> nested_svm_copy_common_state(svm->nested.vmcb02.ptr, svm->vmcb01.ptr);
>
> svm_switch_vmcb(svm, &svm->vmcb01);
...
> +static int bus_lock_exit(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + vcpu->run->exit_reason = KVM_EXIT_X86_BUS_LOCK;
> + vcpu->run->flags |= KVM_RUN_X86_BUS_LOCK;
> +
> + vcpu->arch.cui_linear_rip = kvm_get_linear_rip(vcpu);
> + svm->bus_lock_rip = vcpu->arch.cui_linear_rip;
> + vcpu->arch.complete_userspace_io = complete_userspace_buslock;
> +
> + return 0;
> +}
> @@ -327,6 +328,7 @@ struct vcpu_svm {
>
> /* Guest GIF value, used when vGIF is not enabled */
> bool guest_gif;
> + u64 bus_lock_rip;
I don't think this field is necessary. Rather than unconditionally invalidate
on nested VMRUN and then conditionally restore on nested #VMEXIT, just leave
svm->nested.ctl.bus_lock_rip set on VMRUN and conditionally invalidate on
#VMEXIT.
And then in bus_lock_exit(), update the field if the exit occurred while L2 is
active.
Completely untested:
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index a42ef7dd9143..98e065a93516 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -700,13 +700,10 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm
*svm,
* L1 re-enters L2, the same instruction will trigger a VM-Exit and the
* entire cycle start over.
*/
- if (vmcb02->save.rip && (svm->nested.ctl.bus_lock_rip ==
vmcb02->save.rip)) {
+ if (vmcb02->save.rip && (svm->nested.ctl.bus_lock_rip ==
vmcb02->save.rip))
vmcb02->control.bus_lock_counter = 1;
- svm->bus_lock_rip = svm->nested.ctl.bus_lock_rip;
- } else {
+ else
vmcb02->control.bus_lock_counter = 0;
- }
- svm->nested.ctl.bus_lock_rip = INVALID_GPA;
/* Done at vmrun: asid. */
@@ -1070,15 +1067,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
}
/*
- * If bus_lock_counter is nonzero and the guest has not moved past the
- * guilty instruction, save bus_lock_rip in svm_nested_state. This will
- * help determine at nested VMRUN whether to stash vmcb02's counter or
- * reset it to '0'.
+ * Invalidate bus_lock_rip unless kVM is still waiting for the guest
+ * to make forward progress before re-enabling bus lock detection.
*/
- if (vmcb02->control.bus_lock_counter &&
- svm->bus_lock_rip == vmcb02->save.rip)
- svm->nested.ctl.bus_lock_rip = svm->bus_lock_rip;
- else
+ if (!vmcb02->control.bus_lock_counter)
svm->nested.ctl.bus_lock_rip = INVALID_GPA;
nested_svm_copy_common_state(svm->nested.vmcb02.ptr, svm->vmcb01.ptr);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ea12e93ae983..11ce031323fd 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3333,9 +3333,10 @@ static int bus_lock_exit(struct kvm_vcpu *vcpu)
vcpu->run->flags |= KVM_RUN_X86_BUS_LOCK;
vcpu->arch.cui_linear_rip = kvm_get_linear_rip(vcpu);
- svm->bus_lock_rip = vcpu->arch.cui_linear_rip;
vcpu->arch.complete_userspace_io = complete_userspace_buslock;
+ if (is_guest_mode(vcpu))
+ svm->nested.ctl.bus_lock_rip = vcpu->arch.cui_linear_rip;
return 0;
}
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 7a4c5848c952..8667faccaedc 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -328,7 +328,6 @@ struct vcpu_svm {
/* Guest GIF value, used when vGIF is not enabled */
bool guest_gif;
- u64 bus_lock_rip;
};
struct svm_cpu_data {
