[PATCH v13 20/22] KVM: selftests: Implement MMIO WRITE for the TDX VM

[Lisa Wang]

From: Erdem Aktas <erdemaktas@xxxxxxxxxx>

Implement the tdx_mmio_write() to allow TDX VMs to request MMIO
emulation.

Follow the Intel Guest-Hypervisor Communication Interface (GHCI) spec
to the minimum extent that a spec-abiding TDX module will pass the
request to KVM. Skip implementing the #VE handler as described in the
GHCI spec so selftests will not take a dependency on having a working

To perform emulated I/O, VMs use the TDG.VP.VMCALL instruction to
request MMIO.

Signed-off-by: Erdem Aktas <erdemaktas@xxxxxxxxxx>
Co-developed-by: Sagi Shahar <sagis@xxxxxxxxxx>
Signed-off-by: Sagi Shahar <sagis@xxxxxxxxxx>
Co-developed-by: Lisa Wang <wyihan@xxxxxxxxxx>
Signed-off-by: Lisa Wang <wyihan@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile.kvm          |  1 +
 tools/testing/selftests/kvm/include/x86/tdx/tdx.h | 16 ++++++++++++
 tools/testing/selftests/kvm/lib/x86/tdx/tdx.c     | 30 +++++++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index a651a876c522..489324cecf83 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -33,6 +33,7 @@ LIBKVM_x86 += lib/x86/ucall.c
 LIBKVM_x86 += lib/x86/vmx.c
 LIBKVM_x86 += lib/x86/tdx/tdx_util.c
 LIBKVM_x86 += lib/x86/tdx/td_boot.S
+LIBKVM_x86 += lib/x86/tdx/tdx.c
 
 LIBKVM_arm64 += lib/arm64/gic.c
 LIBKVM_arm64 += lib/arm64/gic_v3.c
diff --git a/tools/testing/selftests/kvm/include/x86/tdx/tdx.h b/tools/testing/selftests/kvm/include/x86/tdx/tdx.h
new file mode 100644
index 000000000000..810ca7423c84
--- /dev/null
+++ b/tools/testing/selftests/kvm/include/x86/tdx/tdx.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef SELFTESTS_TDX_TDX_H
+#define SELFTESTS_TDX_TDX_H
+
+#include <linux/types.h>
+
+enum mmio_size {
+	MMIO_SIZE_1B = 1,
+	MMIO_SIZE_2B = 2,
+	MMIO_SIZE_4B = 4,
+	MMIO_SIZE_8B = 8
+};
+
+u64 tdx_mmio_write(u64 address, enum mmio_size size, u64 data_in);
+
+#endif // SELFTESTS_TDX_TDX_H
diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/tdx.c b/tools/testing/selftests/kvm/lib/x86/tdx/tdx.c
new file mode 100644
index 000000000000..f19be79fe11f
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "tdx/tdx.h"
+
+#define TDG_VP_VMCALL 0
+#define TDG_VP_VMCALL_VE_REQUEST_MMIO    48
+#define TDVMCALL_MMIO_WRITE		  1
+#define TDVMCALL_EXPOSE_REGS_MASK    0xFC00
+
+u64 tdx_mmio_write(u64 address, enum mmio_size size, u64 data_in)
+{
+	register u64 r10_reg asm("r10") = TDG_VP_VMCALL;
+	register u64 r11_reg asm("r11") = TDG_VP_VMCALL_VE_REQUEST_MMIO;
+	register u64 r12_reg asm("r12") = size;
+	register u64 r13_reg asm("r13") = TDVMCALL_MMIO_WRITE;
+	register u64 r14_reg asm("r14") = address;
+	register u64 r15_reg asm("r15") = data_in;
+	register u64 rax_reg asm("rax") = TDG_VP_VMCALL;
+	register u64 rcx_reg asm("rcx") = TDVMCALL_EXPOSE_REGS_MASK;
+
+	asm volatile(
+	 ".byte 0x66,0x0f,0x01,0xcc" /* tdcall */
+	 : "+r" (r10_reg), "+r" (r11_reg)
+	 : "r" (r12_reg), "r" (r13_reg), "r" (r14_reg), "r" (r15_reg),
+	   "r" (rax_reg), "r" (rcx_reg)
+	 : "cc", "memory"
+	);
+
+	return r10_reg;
+}

-- 
2.54.0.746.g67dd491aae-goog