[PATCH v2 6/8] KVM: TDX: Handle TDG.VP.VMCALL<ReportFatalError>

[Binbin Wu <binbin.wu@linux.intel.com>]

Convert TDG.VP.VMCALL<ReportFatalError> to KVM_EXIT_SYSTEM_EVENT with
a new type KVM_SYSTEM_EVENT_TDX_FATAL and forward it to userspace for
handling.

TD guest can use TDG.VP.VMCALL<ReportFatalError> to report the fatal
error it has experienced.  This hypercall is special because TD guest
is requesting a termination with the error information, KVM needs to
forward the hypercall to userspace anyway, KVM doesn't do sanity checks
and let userspace decide what to do.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
Hypercalls exit to userspace v2:
- Use vp_enter_args instead of x86 registers.
- vcpu->run->system_event.ndata is not hardcoded to 10. (Xiaoyao)
- Undefine COPY_REG after use. (Yilun)
- Updated the document about KVM_SYSTEM_EVENT_TDX_FATAL. (Chao)

Hypercalls exit to userspace v1:
- New added.
  Implement one of the hypercalls need to exit to userspace for handling after
  reverting "KVM: TDX: Add KVM Exit for TDX TDG.VP.VMCALL", which tries to resolve
  Sean's comment.
  https://lore.kernel.org/kvm/Zg18ul8Q4PGQMWam@google.com/
- Use TDVMCALL_STATUS prefix for TDX call status codes (Binbin)
---
 Documentation/virt/kvm/api.rst |  9 +++++++
 arch/x86/kvm/vmx/tdx.c         | 45 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  1 +
 3 files changed, 55 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 2ba70c1fad51..5e415b312ab0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6823,6 +6823,7 @@ should put the acknowledged interrupt vector into the 'epr' field.
   #define KVM_SYSTEM_EVENT_WAKEUP         4
   #define KVM_SYSTEM_EVENT_SUSPEND        5
   #define KVM_SYSTEM_EVENT_SEV_TERM       6
+  #define KVM_SYSTEM_EVENT_TDX_FATAL      7
 			__u32 type;
                         __u32 ndata;
                         __u64 data[16];
@@ -6849,6 +6850,14 @@ Valid values for 'type' are:
    reset/shutdown of the VM.
  - KVM_SYSTEM_EVENT_SEV_TERM -- an AMD SEV guest requested termination.
    The guest physical address of the guest's GHCB is stored in `data[0]`.
+ - KVM_SYSTEM_EVENT_TDX_FATAL -- a TDX guest reported a fatal error state.
+   The error code reported by the TDX guest is stored in `data[0]`, the error
+   code format is defined in TDX GHCI specification.
+   If the bit 63 of `data[0]` is set, it indicates there is TD specified
+   additional information provided in a page, which is shared memory. The
+   guest physical address of the information page is stored in `data[1]`.
+   An optional error message is provided by `data[2]` ~ `data[9]`, which is
+   byte sequence, LSB filled first. Typically, ASCII code(0x20-0x7e) is filled.
  - KVM_SYSTEM_EVENT_WAKEUP -- the exiting vCPU is in a suspended state and
    KVM has recognized a wakeup event. Userspace may honor this event by
    marking the exiting vCPU as runnable, or deny it and call KVM_RUN again.
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 8b51b4c937e9..85956768c515 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1092,11 +1092,56 @@ static int tdx_map_gpa(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static int tdx_report_fatal_error(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+	u64 reg_mask = tdx->vp_enter_args.rcx;
+	u64 *opt_regs;
+
+	/*
+	 * Skip sanity checks and let userspace decide what to do if sanity
+	 * checks fail.
+	 */
+	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
+	vcpu->run->system_event.type = KVM_SYSTEM_EVENT_TDX_FATAL;
+	/* Error codes. */
+	vcpu->run->system_event.data[0] = tdx->vp_enter_args.r12;
+	/* GPA of additional information page. */
+	vcpu->run->system_event.data[1] = tdx->vp_enter_args.r13;
+	/* Information passed via registers (up to 64 bytes). */
+	opt_regs = &vcpu->run->system_event.data[2];
+
+#define COPY_REG(REG, MASK)						\
+	do {								\
+		if (reg_mask & MASK) {					\
+			*opt_regs = tdx->vp_enter_args.REG;		\
+			opt_regs++;					\
+		}							\
+	} while (0)
+
+	/* The order is defined in GHCI. */
+	COPY_REG(r14, BIT_ULL(14));
+	COPY_REG(r15, BIT_ULL(15));
+	COPY_REG(rbx, BIT_ULL(3));
+	COPY_REG(rdi, BIT_ULL(7));
+	COPY_REG(rsi, BIT_ULL(6));
+	COPY_REG(r8, BIT_ULL(8));
+	COPY_REG(r9, BIT_ULL(9));
+	COPY_REG(rdx, BIT_ULL(2));
+#undef COPY_REG
+
+	vcpu->run->system_event.ndata = opt_regs - vcpu->run->system_event.data;
+
+	return 0;
+}
+
 static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 {
 	switch (tdvmcall_leaf(vcpu)) {
 	case TDVMCALL_MAP_GPA:
 		return tdx_map_gpa(vcpu);
+	case TDVMCALL_REPORT_FATAL_ERROR:
+		return tdx_report_fatal_error(vcpu);
 	default:
 		break;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 45e6d8fca9b9..937400350317 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -375,6 +375,7 @@ struct kvm_run {
 #define KVM_SYSTEM_EVENT_WAKEUP         4
 #define KVM_SYSTEM_EVENT_SUSPEND        5
 #define KVM_SYSTEM_EVENT_SEV_TERM       6
+#define KVM_SYSTEM_EVENT_TDX_FATAL      7
 			__u32 type;
 			__u32 ndata;
 			union {
-- 
2.46.0