[PATCH 3/3] KVM: arm64: nv: Move to per nested mmu ptdump files

[Wei-Lin Chang]

The previous way of exposing shadow page tables was creating a debugfs
ptdump file whenever a nested mmu instance gets bound to a new context,
and deleting the debugfs file whose context was getting unbound.

This turned out to be buggy, as the instance<->context binding process
is done with the mmu_lock held, and debugfs creation/deletion can sleep.

Instead, create a debugfs file for each nested mmu instance, and show
different information based on what the nested mmu instance is holding
at the moment, which can be either invalid, or VTCR + VTTBR + whether s2
enabled + ptdump.

Fixes: 19e15dc73f0f ("KVM: arm64: nv: Expose shadow page tables in debugfs")
Reported-by: Itaru Kitayama <itaru.kitayama@xxxxxxxxxxx>
Closes: https://lore.kernel.org/kvmarm/aiuF0KSvvv-ZozI1@sm-arm-grace07/
Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
---
 arch/arm64/kvm/nested.c | 16 +++++++++++-----
 arch/arm64/kvm/ptdump.c |  9 +++------
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index bdf12b2ae097..2aaf6c123a20 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -110,6 +110,11 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
 
 		write_unlock(&kvm->mmu_lock);
 
+		for (int i = 0; i < kvm->arch.nested_mmus_size; i++) {
+			kvm_nested_s2_ptdump_remove_debugfs(&tmp[i]);
+			kvm_nested_s2_ptdump_create_debugfs(&kvm->arch.nested_mmus[i]);
+		}
+
 		kvfree(tmp);
 	}
 
@@ -126,6 +131,9 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
 		return ret;
 	}
 
+	for (int i = kvm->arch.nested_mmus_size; i < num_mmus; i++)
+		kvm_nested_s2_ptdump_create_debugfs(&kvm->arch.nested_mmus[i]);
+
 	kvm->arch.nested_mmus_size = num_mmus;
 
 	return 0;
@@ -817,10 +825,8 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
 	kvm->arch.nested_mmus_next = (i + 1) % kvm->arch.nested_mmus_size;
 
 	/* Make sure we don't forget to do the laundry */
-	if (kvm_s2_mmu_valid(s2_mmu)) {
-		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
+	if (kvm_s2_mmu_valid(s2_mmu))
 		s2_mmu->pending_unmap = true;
-	}
 
 	/*
 	 * The virtual VMID (modulo CnP) will be used as a key when matching
@@ -834,8 +840,6 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
 	s2_mmu->tlb_vtcr = vcpu_read_sys_reg(vcpu, VTCR_EL2);
 	s2_mmu->nested_stage2_enabled = vcpu_read_sys_reg(vcpu, HCR_EL2) & HCR_VM;
 
-	kvm_nested_s2_ptdump_create_debugfs(s2_mmu);
-
 out:
 	atomic_inc(&s2_mmu->refcnt);
 
@@ -1275,6 +1279,8 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm)
 	for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
 		struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
 
+		kvm_nested_s2_ptdump_remove_debugfs(mmu);
+
 		if (!WARN_ON(atomic_read(&mmu->refcnt)))
 			kvm_free_stage2_pgd(mmu);
 	}
diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
index a089e87ea366..2a1cbef2375b 100644
--- a/arch/arm64/kvm/ptdump.c
+++ b/arch/arm64/kvm/ptdump.c
@@ -17,7 +17,7 @@
 
 #define MARKERS_LEN		2
 #define KVM_PGTABLE_MAX_LEVELS	(KVM_PGTABLE_LAST_LEVEL + 1)
-#define S2FNAMESZ		sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled")
+#define S2FNAMESZ		sizeof("nested_mmu_9999")
 
 /*
  * Nested mmus could be freed when .release() is called, so also keep the kvm
@@ -287,14 +287,11 @@ static const struct file_operations kvm_pgtable_levels_fops = {
 
 void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
 {
+	int idx = mmu - mmu->arch->nested_mmus;
 	struct dentry *dent;
 	char file_name[S2FNAMESZ];
 
-	snprintf(file_name, sizeof(file_name), "0x%016llx-0x%016llx-s2-%sabled",
-		 mmu->tlb_vttbr,
-		 mmu->tlb_vtcr,
-		 mmu->nested_stage2_enabled ? "en" : "dis");
-
+	snprintf(file_name, sizeof(file_name), "nested_mmu_%d", idx);
 	dent = debugfs_create_file(file_name, 0400,
 				   mmu->arch->debugfs_nv_dentry, mmu,
 				   &kvm_ptdump_guest_fops);
-- 
2.43.0