[PATCH 3/7] KVM: TDX: Handle KVM hypercall with TDG.VP.VMCALL

Binbin Wu
2024-12-01T03:52:08Z

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

Handle KVM hypercall for TDX according to TDX Guest-Host Communication
Interface (GHCI) specification.

The TDX GHCI specification defines the ABI for the guest TD to issue
hypercalls. When R10 is non-zero, it indicates the TDG.VP.VMCALL is
vendor-specific. KVM uses R10 as KVM hypercall number and R11-R14
as 4 arguments, while the error code is returned in R10. Follow the
ABI and handle the KVM hypercall for TDX.

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>
---
Hypercalls exit to userspace breakout:
- Renamed from "KVM: TDX: handle KVM hypercall with TDG.VP.VMCALL" to
"KVM: TDX: Handle KVM hypercall with TDG.VP.VMCALL".
- Update the change log.
- Rebased on Sean's "Prep KVM hypercall handling for TDX" patch set.
https://lore.kernel.org/kvm/20241128004344.4072099-1-seanjc@google.com
- Use the right register (i.e. R10) to set the return code after returning
back from userspace.
---
arch/x86/kvm/vmx/tdx.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 19fd8a5dabd0..4cc55b120ab0 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -957,8 +957,39 @@ static int tdx_handle_triple_fault(struct kvm_vcpu *vcpu)
return 0;
}

+
+static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
+{
+ kvm_r10_write(vcpu, vcpu->run->hypercall.ret);
+ return 1;
+}
+
+static int tdx_emulate_vmcall(struct kvm_vcpu *vcpu)
+{
+ int r;
+
+ /*
+ * ABI for KVM tdvmcall argument:
+ * In Guest-Hypervisor Communication Interface(GHCI) specification,
+ * Non-zero leaf number (R10 != 0) is defined to indicate
+ * vendor-specific. KVM uses this for KVM hypercall. NOTE: KVM
+ * hypercall number starts from one. Zero isn't used for KVM hypercall
+ * number.
+ *
+ * R10: KVM hypercall number
+ * arguments: R11, R12, R13, R14.
+ */
+ r = __kvm_emulate_hypercall(vcpu, r10, r11, r12, r13, r14, true, 0,
+ complete_hypercall_exit);
+
+ return r > 0;
+}
+
static int handle_tdvmcall(struct kvm_vcpu *vcpu)
{
+ if (tdvmcall_exit_type(vcpu))
+ return tdx_emulate_vmcall(vcpu);
+
switch (tdvmcall_leaf(vcpu)) {
default:
break;
--
2.46.0