[PATCH v3 7/9] 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 parsing or
conversion, it just dumps the 16 general-purpose registers to userspace
and let userspace decide what to do.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
Hypercalls exit to userspace v3:
- Dump all 16 general-purpose registers to userspace. (Sean)

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         | 28 ++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  1 +
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 2b52eb77e29c..2d75edc9db4f 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];
@@ -6849,9 +6850,11 @@ 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_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.
+ - KVM_SYSTEM_EVENT_TDX_FATAL -- a TDX guest reported a fatal error state.
+   KVM doesn't do any parsing or conversion, it just dumps 16 general-purpose
+   registers to userspace, in ascending order of the 4-bit indices for x86-64
+   general-purpose registers in instruction encoding, as defined in the Intel
+   SDM.
  - KVM_SYSTEM_EVENT_SUSPEND -- the guest has requested a suspension of
    the VM.
 
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 7b2f4c32f01b..7c8356299a25 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1093,11 +1093,39 @@ 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 *regs = vcpu->run->system_event.data;
+	u64 *module_regs = &tdx->vp_enter_args.r8;
+	int index = VCPU_REGS_RAX;
+
+	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
+	vcpu->run->system_event.type = KVM_SYSTEM_EVENT_TDX_FATAL;
+	vcpu->run->system_event.ndata = 16;
+
+	/* Dump 16 general-purpose registers to userspace in ascending order. */
+	regs[index++] = tdx->vp_enter_ret;
+	regs[index++] = tdx->vp_enter_args.rcx;
+	regs[index++] = tdx->vp_enter_args.rdx;
+	regs[index++] = tdx->vp_enter_args.rbx;
+	regs[index++] = 0;
+	regs[index++] = 0;
+	regs[index++] = tdx->vp_enter_args.rsi;
+	regs[index] = tdx->vp_enter_args.rdi;
+	for (index = 0; index < 8; index++)
+		regs[VCPU_REGS_R8 + index] = module_regs[index];
+
+	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