[PATCH 6.18.y 1/2] KVM: arm64: nv: Fully update VNCR fixmap state in kvm_translate_vncr()

[Sasha Levin <sashal@kernel.org>]

From: Oliver Upton <oupton@kernel.org>

[ Upstream commit 5949004d7032767e8fde1e8c986a33f241b2a192 ]

kvm_translate_vncr() first invalidates the pseudo-TLB entry and
corresponding fixmap in anticipation of installing a new translation.

While the fixmap invalidation does clear the mapping from host stage-1,
it does not clear the L1_VNCR_MAPPED flag. Depending on the state of the
VNCR TLB at vcpu_put(), this could potentially precipitate a BUG_ON() if
vt->cpu is reset.

Share a helper with kvm_vcpu_put_hw_mmu(), ensuring that KVM's view of
the VNCR fixmap is in sync with the state of the VNCR TLB. Give it a
slightly verbose name to make it obvious that it is meant to be used
local to a CPU, unlike other VNCR TLB maintenance.

Fixes: 069a05e535496 ("KVM: arm64: nv: Handle VNCR_EL2-triggered faults")
Signed-off-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20260602235450.103057-3-oupton@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Stable-dep-of: 38640bc32be3 ("KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/arm64/kvm/nested.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index b69df61f145a5..5a297c16bc338 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -771,18 +771,24 @@ void kvm_vcpu_load_hw_mmu(struct kvm_vcpu *vcpu)
 	}
 }
 
+static void this_cpu_reset_vncr_fixmap(struct kvm_vcpu *vcpu)
+{
+	if (!host_data_test_flag(L1_VNCR_MAPPED))
+		return;
+
+	BUG_ON(vcpu->arch.vncr_tlb->cpu != smp_processor_id());
+	BUG_ON(is_hyp_ctxt(vcpu));
+
+	clear_fixmap(vncr_fixmap(vcpu->arch.vncr_tlb->cpu));
+	vcpu->arch.vncr_tlb->cpu = -1;
+	host_data_clear_flag(L1_VNCR_MAPPED);
+	atomic_dec(&vcpu->kvm->arch.vncr_map_count);
+}
+
 void kvm_vcpu_put_hw_mmu(struct kvm_vcpu *vcpu)
 {
 	/* Unconditionally drop the VNCR mapping if we have one */
-	if (host_data_test_flag(L1_VNCR_MAPPED)) {
-		BUG_ON(vcpu->arch.vncr_tlb->cpu != smp_processor_id());
-		BUG_ON(is_hyp_ctxt(vcpu));
-
-		clear_fixmap(vncr_fixmap(vcpu->arch.vncr_tlb->cpu));
-		vcpu->arch.vncr_tlb->cpu = -1;
-		host_data_clear_flag(L1_VNCR_MAPPED);
-		atomic_dec(&vcpu->kvm->arch.vncr_map_count);
-	}
+	this_cpu_reset_vncr_fixmap(vcpu);
 
 	/*
 	 * Keep a reference on the associated stage-2 MMU if the vCPU is
@@ -1244,7 +1250,8 @@ static int kvm_translate_vncr(struct kvm_vcpu *vcpu, bool *is_gmem)
 	 * We also prepare the next walk wilst we're at it.
 	 */
 	scoped_guard(write_lock, &vcpu->kvm->mmu_lock) {
-		invalidate_vncr(vt);
+		this_cpu_reset_vncr_fixmap(vcpu);
+		vt->valid = false;
 
 		vt->wi = (struct s1_walk_info) {
 			.regime	= TR_EL20,
-- 
2.53.0