linux-kernel - [PATCH 7/7] fixup! KVM: TDX: Implement TDX vcpu enter/exit path

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Message-ID: <20250113021322.18991-1-yan.y.zhao@intel.com>
Date: Mon, 13 Jan 2025 10:13:22 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...el.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	isaku.yamahata@...il.com
Subject: [PATCH 7/7] fixup! KVM: TDX: Implement TDX vcpu enter/exit path

Warn on force_immediate_exit in tdx_vcpu_run().

force_immediate_exit requires vCPU entering for events injection with an
immediately exit followed. But The TDX module doesn't guarantee entry, it's
already possible for KVM to _think_ it completely entry to the guest
without actually having done so.

Since KVM never needs to force an immediate exit for TDX, and can't do
direct injection, there's no need to implement force_immediate_exit, i.e.
carrying out the kicking vCPU and event reinjection. Simply warn on
force_immediate_exit.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
 arch/x86/kvm/vmx/tdx.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index baabae95504b..0e684f4683f2 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -999,6 +999,16 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 		return EXIT_FASTPATH_NONE;
 	}
 
+	/*
+	 * force_immediate_exit requires vCPU entering for events injection with
+	 * an immediately exit followed. But The TDX module doesn't guarantee
+	 * entry, it's already possible for KVM to _think_ it completely entry
+	 * to the guest without actually having done so.
+	 * Since KVM never needs to force an immediate exit for TDX, and can't
+	 * do direct injection, just warn on force_immediate_exit.
+	 */
+	WARN_ON_ONCE(force_immediate_exit);
+
 	/*
 	 * Wait until retry of SEPT-zap-related SEAMCALL completes before
 	 * allowing vCPU entry to avoid contention with tdh_vp_enter() and
-- 
2.43.2