diff mbox series

[RFC,v6,093/104] KVM: TDX: Handle TDX PV MMIO hypercall

Message ID ea5e6a1fc740cfe69167c8713b63fdb952a98e8b.1651774251.git.isaku.yamahata@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM TDX basic feature support | expand

Commit Message

Isaku Yamahata May 5, 2022, 6:15 p.m. UTC 
From: Sean Christopherson <sean.j.christopherson@intel.com>

Export kvm_io_bus_read and kvm_mmio tracepoint and wire up TDX PV MMIO
hypercall to the KVM backend functions.

kvm_io_bus_read/write() searches KVM device emulated in kernel of the given
MMIO address and emulates the MMIO.  As TDX PV MMIO also needs it, export
kvm_io_bus_read().  kvm_io_bus_write() is already exported.  TDX PV MMIO
emulates some of MMIO itself.  To add trace point consistently with x86
kvm, export kvm_mmio tracepoint.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/tdx.c | 114 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c     |   1 +
 virt/kvm/kvm_main.c    |   2 +
 3 files changed, 117 insertions(+)

Comments

Sagi Shahar June 14, 2022, 6:08 p.m. UTC | #1 
On Thu, May 5, 2022 at 11:16 AM <isaku.yamahata@intel.com> wrote:
>
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Export kvm_io_bus_read and kvm_mmio tracepoint and wire up TDX PV MMIO
> hypercall to the KVM backend functions.
>
> kvm_io_bus_read/write() searches KVM device emulated in kernel of the given
> MMIO address and emulates the MMIO.  As TDX PV MMIO also needs it, export
> kvm_io_bus_read().  kvm_io_bus_write() is already exported.  TDX PV MMIO
> emulates some of MMIO itself.  To add trace point consistently with x86
> kvm, export kvm_mmio tracepoint.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 114 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/x86.c     |   1 +
>  virt/kvm/kvm_main.c    |   2 +
>  3 files changed, 117 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index ee0cf5336ade..6ab4a52fc9e9 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1057,6 +1057,118 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
>         return ret;
>  }
>
> +static int tdx_complete_mmio(struct kvm_vcpu *vcpu)
> +{
> +       unsigned long val = 0;
> +       gpa_t gpa;
> +       int size;
> +
> +       WARN_ON(vcpu->mmio_needed != 1);
> +       vcpu->mmio_needed = 0;
> +
> +       if (!vcpu->mmio_is_write) {
> +               gpa = vcpu->mmio_fragments[0].gpa;
> +               size = vcpu->mmio_fragments[0].len;
> +
> +               memcpy(&val, vcpu->run->mmio.data, size);
> +               tdvmcall_set_return_val(vcpu, val);
> +               trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> +       }
> +       return 1;
> +}
> +
> +static inline int tdx_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, int size,
> +                                unsigned long val)
> +{
> +       if (kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> +           kvm_io_bus_write(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> +               return -EOPNOTSUPP;
> +
> +       trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val);
> +       return 0;
> +}
> +
> +static inline int tdx_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
> +{
> +       unsigned long val;
> +
> +       if (kvm_iodevice_read(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> +           kvm_io_bus_read(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> +               return -EOPNOTSUPP;
> +
> +       tdvmcall_set_return_val(vcpu, val);
> +       trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> +       return 0;
> +}
> +
> +static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
> +{
> +       struct kvm_memory_slot *slot;
> +       int size, write, r;
> +       unsigned long val;
> +       gpa_t gpa;
> +
> +       WARN_ON(vcpu->mmio_needed);
> +
> +       size = tdvmcall_a0_read(vcpu);
> +       write = tdvmcall_a1_read(vcpu);
> +       gpa = tdvmcall_a2_read(vcpu);
> +       val = write ? tdvmcall_a3_read(vcpu) : 0;
> +
> +       if (size != 1 && size != 2 && size != 4 && size != 8)
> +               goto error;
> +       if (write != 0 && write != 1)
> +               goto error;
> +
> +       /* Strip the shared bit, allow MMIO with and without it set. */
> +       gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
> +
> +       if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
> +               goto error;
> +
> +       slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
> +       if (slot && !(slot->flags & KVM_MEMSLOT_INVALID))
> +               goto error;
> +
> +       if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
> +               trace_kvm_fast_mmio(gpa);
> +               return 1;
> +       }
> +
> +       if (write)
> +               r = tdx_mmio_write(vcpu, gpa, size, val);
> +       else
> +               r = tdx_mmio_read(vcpu, gpa, size);
> +       if (!r) {
> +               /* Kernel completed device emulation. */
> +               tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
> +               return 1;
> +       }
> +
> +       /* Request the device emulation to userspace device model. */
> +       vcpu->mmio_needed = 1;
> +       vcpu->mmio_is_write = write;
> +       vcpu->arch.complete_userspace_io = tdx_complete_mmio;
> +
> +       vcpu->run->mmio.phys_addr = gpa;
> +       vcpu->run->mmio.len = size;
> +       vcpu->run->mmio.is_write = write;
> +       vcpu->run->exit_reason = KVM_EXIT_MMIO;
> +
> +       if (write) {
> +               memcpy(vcpu->run->mmio.data, &val, size);
> +       } else {
> +               vcpu->mmio_fragments[0].gpa = gpa;
> +               vcpu->mmio_fragments[0].len = size;
> +               trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
> +       }
> +       return 0;
> +
> +error:
> +       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);

We should return an error code here.

> +       return 1;
> +}
> +
>  static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>  {
>         if (tdvmcall_exit_type(vcpu))
> @@ -1069,6 +1181,8 @@ static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>                 return tdx_emulate_hlt(vcpu);
>         case EXIT_REASON_IO_INSTRUCTION:
>                 return tdx_emulate_io(vcpu);
> +       case EXIT_REASON_EPT_VIOLATION:
> +               return tdx_emulate_mmio(vcpu);
>         default:
>                 break;
>         }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5f291470a6f6..f367d0dcef97 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -13166,6 +13166,7 @@ bool kvm_arch_dirty_log_supported(struct kvm *kvm)
>
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_mmio);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4bf7178e42bd..7f01131666de 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2294,6 +2294,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
>
>         return NULL;
>  }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
>
>  bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
>  {
> @@ -5169,6 +5170,7 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
>         r = __kvm_io_bus_read(vcpu, bus, &range, val);
>         return r < 0 ? r : 0;
>  }
> +EXPORT_SYMBOL_GPL(kvm_io_bus_read);
>
>  /* Caller must hold slots_lock. */
>  int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> --
> 2.25.1
>

Sagi
Isaku Yamahata June 29, 2022, 10:17 a.m. UTC | #2 
On Tue, Jun 14, 2022 at 11:08:16AM -0700,
Sagi Shahar <sagis@google.com> wrote:

> On Thu, May 5, 2022 at 11:16 AM <isaku.yamahata@intel.com> wrote:
> >
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> >
> > Export kvm_io_bus_read and kvm_mmio tracepoint and wire up TDX PV MMIO
> > hypercall to the KVM backend functions.
> >
> > kvm_io_bus_read/write() searches KVM device emulated in kernel of the given
> > MMIO address and emulates the MMIO.  As TDX PV MMIO also needs it, export
> > kvm_io_bus_read().  kvm_io_bus_write() is already exported.  TDX PV MMIO
> > emulates some of MMIO itself.  To add trace point consistently with x86
> > kvm, export kvm_mmio tracepoint.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  arch/x86/kvm/vmx/tdx.c | 114 +++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/x86.c     |   1 +
> >  virt/kvm/kvm_main.c    |   2 +
> >  3 files changed, 117 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index ee0cf5336ade..6ab4a52fc9e9 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -1057,6 +1057,118 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
> >         return ret;
> >  }
> >
> > +static int tdx_complete_mmio(struct kvm_vcpu *vcpu)
> > +{
> > +       unsigned long val = 0;
> > +       gpa_t gpa;
> > +       int size;
> > +
> > +       WARN_ON(vcpu->mmio_needed != 1);
> > +       vcpu->mmio_needed = 0;
> > +
> > +       if (!vcpu->mmio_is_write) {
> > +               gpa = vcpu->mmio_fragments[0].gpa;
> > +               size = vcpu->mmio_fragments[0].len;
> > +
> > +               memcpy(&val, vcpu->run->mmio.data, size);
> > +               tdvmcall_set_return_val(vcpu, val);
> > +               trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> > +       }
> > +       return 1;
> > +}
> > +
> > +static inline int tdx_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, int size,
> > +                                unsigned long val)
> > +{
> > +       if (kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> > +           kvm_io_bus_write(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> > +               return -EOPNOTSUPP;
> > +
> > +       trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val);
> > +       return 0;
> > +}
> > +
> > +static inline int tdx_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
> > +{
> > +       unsigned long val;
> > +
> > +       if (kvm_iodevice_read(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> > +           kvm_io_bus_read(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> > +               return -EOPNOTSUPP;
> > +
> > +       tdvmcall_set_return_val(vcpu, val);
> > +       trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> > +       return 0;
> > +}
> > +
> > +static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
> > +{
> > +       struct kvm_memory_slot *slot;
> > +       int size, write, r;
> > +       unsigned long val;
> > +       gpa_t gpa;
> > +
> > +       WARN_ON(vcpu->mmio_needed);
> > +
> > +       size = tdvmcall_a0_read(vcpu);
> > +       write = tdvmcall_a1_read(vcpu);
> > +       gpa = tdvmcall_a2_read(vcpu);
> > +       val = write ? tdvmcall_a3_read(vcpu) : 0;
> > +
> > +       if (size != 1 && size != 2 && size != 4 && size != 8)
> > +               goto error;
> > +       if (write != 0 && write != 1)
> > +               goto error;
> > +
> > +       /* Strip the shared bit, allow MMIO with and without it set. */
> > +       gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
> > +
> > +       if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
> > +               goto error;
> > +
> > +       slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
> > +       if (slot && !(slot->flags & KVM_MEMSLOT_INVALID))
> > +               goto error;
> > +
> > +       if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
> > +               trace_kvm_fast_mmio(gpa);
> > +               return 1;
> > +       }
> > +
> > +       if (write)
> > +               r = tdx_mmio_write(vcpu, gpa, size, val);
> > +       else
> > +               r = tdx_mmio_read(vcpu, gpa, size);
> > +       if (!r) {
> > +               /* Kernel completed device emulation. */
> > +               tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
> > +               return 1;
> > +       }
> > +
> > +       /* Request the device emulation to userspace device model. */
> > +       vcpu->mmio_needed = 1;
> > +       vcpu->mmio_is_write = write;
> > +       vcpu->arch.complete_userspace_io = tdx_complete_mmio;
> > +
> > +       vcpu->run->mmio.phys_addr = gpa;
> > +       vcpu->run->mmio.len = size;
> > +       vcpu->run->mmio.is_write = write;
> > +       vcpu->run->exit_reason = KVM_EXIT_MMIO;
> > +
> > +       if (write) {
> > +               memcpy(vcpu->run->mmio.data, &val, size);
> > +       } else {
> > +               vcpu->mmio_fragments[0].gpa = gpa;
> > +               vcpu->mmio_fragments[0].len = size;
> > +               trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
> > +       }
> > +       return 0;
> > +
> > +error:
> > +       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
> 
> We should return an error code here.

Yes, I'll fix it as follows. Thanks for catching it.

 error:
-       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
+       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_INVALID_OPERAND);
        return 1;
 }
diff mbox series

Patch

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index ee0cf5336ade..6ab4a52fc9e9 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1057,6 +1057,118 @@  static int tdx_emulate_io(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
+static int tdx_complete_mmio(struct kvm_vcpu *vcpu)
+{
+	unsigned long val = 0;
+	gpa_t gpa;
+	int size;
+
+	WARN_ON(vcpu->mmio_needed != 1);
+	vcpu->mmio_needed = 0;
+
+	if (!vcpu->mmio_is_write) {
+		gpa = vcpu->mmio_fragments[0].gpa;
+		size = vcpu->mmio_fragments[0].len;
+
+		memcpy(&val, vcpu->run->mmio.data, size);
+		tdvmcall_set_return_val(vcpu, val);
+		trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
+	}
+	return 1;
+}
+
+static inline int tdx_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, int size,
+				 unsigned long val)
+{
+	if (kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
+	    kvm_io_bus_write(vcpu, KVM_MMIO_BUS, gpa, size, &val))
+		return -EOPNOTSUPP;
+
+	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val);
+	return 0;
+}
+
+static inline int tdx_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
+{
+	unsigned long val;
+
+	if (kvm_iodevice_read(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
+	    kvm_io_bus_read(vcpu, KVM_MMIO_BUS, gpa, size, &val))
+		return -EOPNOTSUPP;
+
+	tdvmcall_set_return_val(vcpu, val);
+	trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
+	return 0;
+}
+
+static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
+{
+	struct kvm_memory_slot *slot;
+	int size, write, r;
+	unsigned long val;
+	gpa_t gpa;
+
+	WARN_ON(vcpu->mmio_needed);
+
+	size = tdvmcall_a0_read(vcpu);
+	write = tdvmcall_a1_read(vcpu);
+	gpa = tdvmcall_a2_read(vcpu);
+	val = write ? tdvmcall_a3_read(vcpu) : 0;
+
+	if (size != 1 && size != 2 && size != 4 && size != 8)
+		goto error;
+	if (write != 0 && write != 1)
+		goto error;
+
+	/* Strip the shared bit, allow MMIO with and without it set. */
+	gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
+
+	if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
+		goto error;
+
+	slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
+	if (slot && !(slot->flags & KVM_MEMSLOT_INVALID))
+		goto error;
+
+	if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
+		trace_kvm_fast_mmio(gpa);
+		return 1;
+	}
+
+	if (write)
+		r = tdx_mmio_write(vcpu, gpa, size, val);
+	else
+		r = tdx_mmio_read(vcpu, gpa, size);
+	if (!r) {
+		/* Kernel completed device emulation. */
+		tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
+		return 1;
+	}
+
+	/* Request the device emulation to userspace device model. */
+	vcpu->mmio_needed = 1;
+	vcpu->mmio_is_write = write;
+	vcpu->arch.complete_userspace_io = tdx_complete_mmio;
+
+	vcpu->run->mmio.phys_addr = gpa;
+	vcpu->run->mmio.len = size;
+	vcpu->run->mmio.is_write = write;
+	vcpu->run->exit_reason = KVM_EXIT_MMIO;
+
+	if (write) {
+		memcpy(vcpu->run->mmio.data, &val, size);
+	} else {
+		vcpu->mmio_fragments[0].gpa = gpa;
+		vcpu->mmio_fragments[0].len = size;
+		trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
+	}
+	return 0;
+
+error:
+	tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
+	return 1;
+}
+
 static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 {
 	if (tdvmcall_exit_type(vcpu))
@@ -1069,6 +1181,8 @@  static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 		return tdx_emulate_hlt(vcpu);
 	case EXIT_REASON_IO_INSTRUCTION:
 		return tdx_emulate_io(vcpu);
+	case EXIT_REASON_EPT_VIOLATION:
+		return tdx_emulate_mmio(vcpu);
 	default:
 		break;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5f291470a6f6..f367d0dcef97 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13166,6 +13166,7 @@  bool kvm_arch_dirty_log_supported(struct kvm *kvm)
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
+EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_mmio);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4bf7178e42bd..7f01131666de 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2294,6 +2294,7 @@  struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
 
 	return NULL;
 }
+EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
 
 bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 {
@@ -5169,6 +5170,7 @@  int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
 	r = __kvm_io_bus_read(vcpu, bus, &range, val);
 	return r < 0 ? r : 0;
 }
+EXPORT_SYMBOL_GPL(kvm_io_bus_read);
 
 /* Caller must hold slots_lock. */
 int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,