Re: [PATCH 1/7] KVM: TDX: Add a place holder to handle TDX VM exit
From: Binbin Wu
Date: Mon Dec 09 2024 - 21:16:48 EST
On 12/9/2024 7:21 PM, Chao Gao wrote:
On Sun, Dec 01, 2024 at 11:53:50AM +0800, Binbin Wu wrote:
From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Introduce the wiring for handling TDX VM exits by implementing the
callbacks .get_exit_info(), and .handle_exit(). Additionally, add
error handling during the TDX VM exit flow, and add a place holder
to handle various exit reasons. Add helper functions to retrieve
exit information, exit qualifications, and more.
Contention Handling: The TDH.VP.ENTER operation may contend with TDH.MEM.*
operations for secure EPT or TD EPOCH. If contention occurs, the return
value will have TDX_OPERAND_BUSY set with operand type, prompting the vCPU
to attempt re-entry into the guest via the fast path.
Error Handling: The following scenarios will return to userspace with
KVM_EXIT_INTERNAL_ERROR.
- TDX_SW_ERROR: This includes #UD caused by SEAMCALL instruction if the
CPU isn't in VMX operation, #GP caused by SEAMCALL instruction when TDX
isn't enabled by the BIOS, and TDX_SEAMCALL_VMFAILINVALID when SEAM
firmware is not loaded or disabled.
- TDX_ERROR: This indicates some check failed in the TDX module, preventing
the vCPU from running.
- TDX_NON_RECOVERABLE: Set by the TDX module when the error is
non-recoverable, indicating that the TDX guest is dead or the vCPU is
disabled. This also covers failed_vmentry case, which must have
TDX_NON_RECOVERABLE set since off-TD debug feature has not been enabled.
An exception is the triple fault, which also sets TDX_NON_RECOVERABLE
but exits to userspace with KVM_EXIT_SHUTDOWN, aligning with the VMX
case.
- Any unhandled VM exit reason will also return to userspace with
KVM_EXIT_INTERNAL_ERROR.
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Co-developed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
[..]
fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
{
struct vcpu_tdx *tdx = to_tdx(vcpu);
@@ -837,9 +900,26 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
tdx->prep_switch_state = TDX_PREP_SW_STATE_UNRESTORED;
vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
+
+ if (unlikely((tdx->vp_enter_ret & TDX_SW_ERROR) == TDX_SW_ERROR))
+ return EXIT_FASTPATH_NONE;
+
+ if (unlikely(tdx_check_exit_reason(vcpu, EXIT_REASON_MCE_DURING_VMENTRY)))
+ kvm_machine_check();
I was wandering if EXIT_REASON_MCE_DURING_VMENTRY should be handled in the
switch-case in tdx_handle_exit() because I saw there is a dedicated handler
for VMX. But looks EXIT_REASON_MCE_DURING_VMENTRY is a kind of VMentry
failure. So, it won't reach that switch-case.
Yes, similar to VMX, for TDX, EXIT_REASON_MCE_DURING_VMENTRY will be captured
by failed_vmentry, which will have TDX_NON_RECOVERABLE set and handled before
the switch-case.
And, VMX's handler for
EXIT_REASON_MCE_DURING_VMENTRY is actually dead code and can be removed.
I think so, for VMX, the exit_reason.failed_vmentry case will return to
userspace, it won't reach the handler for EXIT_REASON_MCE_DURING_VMENTRY.
+
trace_kvm_exit(vcpu, KVM_ISA_VMX);
- return EXIT_FASTPATH_NONE;
+ if (unlikely(tdx_has_exit_reason(vcpu) && tdexit_exit_reason(vcpu).failed_vmentry))
+ return EXIT_FASTPATH_NONE;
+
+ return tdx_exit_handlers_fastpath(vcpu);
+}
+
+static int tdx_handle_triple_fault(struct kvm_vcpu *vcpu)
+{
+ vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
+ vcpu->mmio_needed = 0;
+ return 0;
}
void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int pgd_level)
@@ -1135,6 +1215,88 @@ int tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
return tdx_sept_drop_private_spte(kvm, gfn, level, pfn);
}
+int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
+{
+ struct vcpu_tdx *tdx = to_tdx(vcpu);
+ u64 vp_enter_ret = tdx->vp_enter_ret;
+ union vmx_exit_reason exit_reason;
+
+ if (fastpath != EXIT_FASTPATH_NONE)
+ return 1;
+
+ /*
+ * Handle TDX SW errors, including TDX_SEAMCALL_UD, TDX_SEAMCALL_GP and
+ * TDX_SEAMCALL_VMFAILINVALID.
+ */
+ if (unlikely((vp_enter_ret & TDX_SW_ERROR) == TDX_SW_ERROR)) {
+ KVM_BUG_ON(!kvm_rebooting, vcpu->kvm);
+ goto unhandled_exit;
+ }
+
+ /*
+ * Without off-TD debug enabled, failed_vmentry case must have
+ * TDX_NON_RECOVERABLE set.
+ */
+ if (unlikely(vp_enter_ret & (TDX_ERROR | TDX_NON_RECOVERABLE))) {
+ /* Triple fault is non-recoverable. */
+ if (unlikely(tdx_check_exit_reason(vcpu, EXIT_REASON_TRIPLE_FAULT)))
+ return tdx_handle_triple_fault(vcpu);
+
+ kvm_pr_unimpl("TD vp_enter_ret 0x%llx, hkid 0x%x hkid pa 0x%llx\n",
+ vp_enter_ret, to_kvm_tdx(vcpu->kvm)->hkid,
+ set_hkid_to_hpa(0, to_kvm_tdx(vcpu->kvm)->hkid));
+ goto unhandled_exit;
+ }
+
+ /* From now, the seamcall status should be TDX_SUCCESS. */
+ WARN_ON_ONCE((vp_enter_ret & TDX_SEAMCALL_STATUS_MASK) != TDX_SUCCESS);
+ exit_reason = tdexit_exit_reason(vcpu);
+
+ switch (exit_reason.basic) {
+ default:
+ break;
+ }
+
+unhandled_exit:
+ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+ vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
+ vcpu->run->internal.ndata = 2;
+ vcpu->run->internal.data[0] = vp_enter_ret;
+ vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
+ return 0;
+}
+
+void tdx_get_exit_info(struct kvm_vcpu *vcpu, u32 *reason,
+ u64 *info1, u64 *info2, u32 *intr_info, u32 *error_code)
+{
+ struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+ if (tdx_has_exit_reason(vcpu)) {
+ /*
+ * Encode some useful info from the the 64 bit return code
+ * into the 32 bit exit 'reason'. If the VMX exit reason is
+ * valid, just set it to those bits.
+ */
+ *reason = (u32)tdx->vp_enter_ret;
+ *info1 = tdexit_exit_qual(vcpu);
+ *info2 = tdexit_ext_exit_qual(vcpu);
+ } else {
+ /*
+ * When the VMX exit reason in vp_enter_ret is not valid,
+ * overload the VMX_EXIT_REASONS_FAILED_VMENTRY bit (31) to
+ * mean the vmexit code is not valid. Set the other bits to
+ * try to avoid picking a value that may someday be a valid
+ * VMX exit code.
+ */
+ *reason = 0xFFFFFFFF;
+ *info1 = 0;
+ *info2 = 0;
+ }
+
+ *intr_info = tdexit_intr_info(vcpu);
If there is no valid exit reason, shouldn't intr_info be set to 0?
Yes. Will fix it.
Thanks!
+ *error_code = 0;
+}
+