[PATCH v2 7/8] KVM: TDX: Handle TDX PV port I/O hypercall

Binbin Wu
2025-02-11T02:53:30Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

Emulate port I/O requested by TDX guest via TDVMCALL with leaf
Instruction.IO (same value as EXIT_REASON_IO_INSTRUCTION) according to
TDX Guest Host Communication Interface (GHCI).

All port I/O instructions inside the TDX guest trigger the #VE exception.
On #VE triggered by I/O instructions, TDX guest can call TDVMCALL with
leaf Instruction.IO to request VMM to emulate I/O instructions.

Similar to normal port I/O emulation, try to handle the port I/O in kernel
first, if kernel can't support it, forward the request to userspace.

Note string I/O operations are not supported in TDX. Guest should unroll
them before calling the TDVMCALL.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
Hypercalls exit to userspace v2:
- Morph PV port I/O hypercall to EXIT_REASON_IO_INSTRUCTION. (Sean)
- Use vp_enter_args instead of x86 registers.
- Check write is either 0 or 1. (Chao)
- Skip setting return code as TDVMCALL_STATUS_SUCCESS. (Sean)

Hypercalls exit to userspace v1:
- Renamed from "KVM: TDX: Handle TDX PV port io hypercall" to
"KVM: TDX: Handle TDX PV port I/O hypercall".
- Update changelog.
- Add missing curly brackets.
- Move reset of pio.count to tdx_complete_pio_out() and remove the stale
comment. (binbin)
- Use TDVMCALL_STATUS prefix for TDX call status codes (Binbin)
- Set status code to TDVMCALL_STATUS_SUCCESS when PIO is handled in kernel.
- Don't write to R11 when it is a write operation for output.

v18:
- Fix out case to set R10 and R11 correctly when user space handled port
out.
---
arch/x86/kvm/vmx/tdx.c | 60 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 85956768c515..f13da28dd4a2 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1135,6 +1135,64 @@ static int tdx_report_fatal_error(struct kvm_vcpu *vcpu)
return 0;
}

+static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.pio.count = 0;
+ return 1;
+}
+
+static int tdx_complete_pio_in(struct kvm_vcpu *vcpu)
+{
+ struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+ unsigned long val = 0;
+ int ret;
+
+ ret = ctxt->ops->pio_in_emulated(ctxt, vcpu->arch.pio.size,
+ vcpu->arch.pio.port, &val, 1);
+
+ WARN_ON_ONCE(!ret);
+
+ tdvmcall_set_return_val(vcpu, val);
+
+ return 1;
+}
+
+static int tdx_emulate_io(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_tdx *tdx = to_tdx(vcpu);
+ struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+ unsigned long val = 0;
+ unsigned int port;
+ u64 size, write;
+ int ret;
+
+ ++vcpu->stat.io_exits;
+
+ size = tdx->vp_enter_args.r12;
+ write = tdx->vp_enter_args.r13;
+ port = tdx->vp_enter_args.r14;
+
+ if ((write != 0 && write != 1) || (size != 1 && size != 2 && size != 4)) {
+ tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
+ return 1;
+ }
+
+ if (write) {
+ val = tdx->vp_enter_args.r15;
+ ret = ctxt->ops->pio_out_emulated(ctxt, size, port, &val, 1);
+ } else {
+ ret = ctxt->ops->pio_in_emulated(ctxt, size, port, &val, 1);
+ }
+
+ if (!ret)
+ vcpu->arch.complete_userspace_io = write ? tdx_complete_pio_out :
+ tdx_complete_pio_in;
+ else if (!write)
+ tdvmcall_set_return_val(vcpu, val);
+
+ return ret;
+}
+
static int handle_tdvmcall(struct kvm_vcpu *vcpu)
{
switch (tdvmcall_leaf(vcpu)) {
@@ -1486,6 +1544,8 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
return handle_tdvmcall(vcpu);
case EXIT_REASON_VMCALL:
return tdx_emulate_vmcall(vcpu);
+ case EXIT_REASON_IO_INSTRUCTION:
+ return tdx_emulate_io(vcpu);
default:
break;
}
--
2.46.0