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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
        Sean Christopherson <seanjc@google.com>,
        Sagi Shahar <sagis@google.com>,
        David Matlack <dmatlack@google.com>,
        Kai Huang <kai.huang@intel.com>,
        Zhi Wang <zhi.wang.linux@gmail.com>, chen.bo@intel.com,
        hang.yuan@intel.com, tina.zhang@intel.com
Subject: [PATCH v16 087/116] KVM: TDX: Handle EXIT_REASON_OTHER_SMI with MSMI
Date:   Mon, 16 Oct 2023 09:14:39 -0700
Message-Id: <f9c047ba60eb29b49ab3756608a5e4c7333f8230.1697471314.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

When BIOS eMCA MCE-SMI morphing is enabled, the #MC is morphed to MSMI
(Machine Check System Management Interrupt).  Then the SMI causes TD exit
with the read reason of EXIT_REASON_OTHER_SMI with MSMI bit set in the exit
qualification to KVM instead of EXIT_REASON_EXCEPTION_NMI with MC
exception.

Handle EXIT_REASON_OTHER_SMI with MSMI bit set in the exit qualification as
MCE(Machine Check Exception) happened during TD guest running.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/vmx/tdx.c      | 40 ++++++++++++++++++++++++++++++++++---
 arch/x86/kvm/vmx/tdx_arch.h |  2 ++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 6bed75c4069c..44558f1c13e4 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -890,6 +890,30 @@ void tdx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
 						     tdexit_intr_info(vcpu));
 	else if (exit_reason == EXIT_REASON_EXCEPTION_NMI)
 		vmx_handle_exception_irqoff(vcpu, tdexit_intr_info(vcpu));
+	else if (unlikely(tdx->exit_reason.non_recoverable ||
+		 tdx->exit_reason.error)) {
+		/*
+		 * The only reason it gets EXIT_REASON_OTHER_SMI is there is an
+		 * #MSMI(Machine Check System Management Interrupt) with
+		 * exit_qualification bit 0 set in TD guest.
+		 * The #MSMI is delivered right after SEAMCALL returns,
+		 * and an #MC is delivered to host kernel after SMI handler
+		 * returns.
+		 *
+		 * The #MC right after SEAMCALL is fixed up and skipped in #MC
+		 * handler because it's an #MC happens in TD guest we cannot
+		 * handle it with host's context.
+		 *
+		 * Call KVM's machine check handler explicitly here.
+		 */
+		if (tdx->exit_reason.basic == EXIT_REASON_OTHER_SMI) {
+			unsigned long exit_qual;
+
+			exit_qual = tdexit_exit_qual(vcpu);
+			if (exit_qual & TD_EXIT_OTHER_SMI_IS_MSMI)
+				kvm_machine_check();
+		}
+	}
 }
 
 static int tdx_handle_exception(struct kvm_vcpu *vcpu)
@@ -1372,6 +1396,11 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
 			      exit_reason.full, exit_reason.basic,
 			      to_kvm_tdx(vcpu->kvm)->hkid,
 			      set_hkid_to_hpa(0, to_kvm_tdx(vcpu->kvm)->hkid));
+
+		/*
+		 * tdx_handle_exit_irqoff() handled EXIT_REASON_OTHER_SMI.  It
+		 * must be handled before enabling preemption because it's #MC.
+		 */
 		goto unhandled_exit;
 	}
 
@@ -1410,9 +1439,14 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
 		return tdx_handle_ept_misconfig(vcpu);
 	case EXIT_REASON_OTHER_SMI:
 		/*
-		 * If reach here, it's not a Machine Check System Management
-		 * Interrupt(MSMI).  #SMI is delivered and handled right after
-		 * SEAMRET, nothing needs to be done in KVM.
+		 * Unlike VMX, all the SMI in SEAM non-root mode (i.e. when
+		 * TD guest vcpu is running) will cause TD exit to TDX module,
+		 * then SEAMRET to KVM. Once it exits to KVM, SMI is delivered
+		 * and handled right away.
+		 *
+		 * - If it's an Machine Check System Management Interrupt
+		 *   (MSMI), it's handled above due to non_recoverable bit set.
+		 * - If it's not an MSMI, don't need to do anything here.
 		 */
 		return 1;
 	default:
diff --git a/arch/x86/kvm/vmx/tdx_arch.h b/arch/x86/kvm/vmx/tdx_arch.h
index fc9a8898765c..9f93250d22b9 100644
--- a/arch/x86/kvm/vmx/tdx_arch.h
+++ b/arch/x86/kvm/vmx/tdx_arch.h
@@ -47,6 +47,8 @@
 #define TDG_VP_VMCALL_REPORT_FATAL_ERROR		0x10003
 #define TDG_VP_VMCALL_SETUP_EVENT_NOTIFY_INTERRUPT	0x10004
 
+#define TD_EXIT_OTHER_SMI_IS_MSMI	BIT(1)
+
 /* TDX control structure (TDR/TDCS/TDVPS) field access codes */
 #define TDX_NON_ARCH			BIT_ULL(63)
 #define TDX_CLASS_SHIFT			56
-- 
2.25.1