[PATCH v2 2/3] KVM: TDX: Do not retry locally when the retry is caused by invalid memslot

[Yan Zhao <yan.y.zhao@intel.com>]

From: Sean Christopherson <seanjc@google.com>

Avoid local retries within the TDX EPT violation handler if a retry is
triggered by faulting in an invalid memslot, indicating that the memslot is
undergoing a removal process.

This prevents the slot removal process from being blocked while waiting for
the VMExit handler to release the SRCU lock.

Opportunistically, export symbol kvm_vcpu_gfn_to_memslot() to allow for
per-vCPU acceleration of gfn_to_memslot translation.

[Yan: Wrote patch log, comment, fixed a minor error, function export]

Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Closes: https://lore.kernel.org/all/20250519023737.30360-1-yan.y.zhao@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
 arch/x86/kvm/vmx/tdx.c | 11 +++++++++++
 virt/kvm/kvm_main.c    |  1 +
 2 files changed, 12 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 6784aaaced87..de2c4bb36069 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1992,6 +1992,11 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
 	 * blocked by TDs, false positives are inevitable i.e., KVM may re-enter
 	 * the guest even if the IRQ/NMI can't be delivered.
 	 *
+	 * Breaking out of the local retries if a retry is caused by faulting
+	 * in an invalid memslot (indicating the slot is under removal), so that
+	 * the slot removal will not be blocked due to waiting for releasing
+	 * SRCU lock in the VMExit handler.
+	 *
 	 * Note: even without breaking out of local retries, zero-step
 	 * mitigation may still occur due to
 	 * - invoking of TDH.VP.ENTER after KVM_EXIT_MEMORY_FAULT,
@@ -2002,6 +2007,8 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
 	 * handle retries locally in their EPT violation handlers.
 	 */
 	while (1) {
+		struct kvm_memory_slot *slot;
+
 		ret = __vmx_handle_ept_violation(vcpu, gpa, exit_qual);
 
 		if (ret != RET_PF_RETRY || !local_retry)
@@ -2015,6 +2022,10 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
 			break;
 		}
 
+		slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
+		if (slot && slot->flags & KVM_MEMSLOT_INVALID)
+			break;
+
 		cond_resched();
 	}
 	return ret;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6c07dd423458..f769d1dccc21 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2661,6 +2661,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
 
 	return NULL;
 }
+EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
 
 bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 {
-- 
2.43.2