[PATCH v2 6/6] KVM: arm64: ptdump: Introduce the shadow ptdump file

[Wei-Lin Chang]

On Wed, Jul 01, 2026 at 04:28:35PM +0100, Leonardo Bras wrote:
> On Tue, Jun 30, 2026 at 01:10:05PM +0100, Wei-Lin Chang wrote:
> > Create a ptdump file for all shadow page tables. It will dump out all
> > valid shadow page tables at the time of request, with the mmu's index,
> > guest VTCR_EL2, VTTBR_EL2, and whether the guest stage-2 is enabled or
> > not.
> > 
> > Also detach the nested mmu array under the mmu_lock in
> > kvm_arch_flush_shadow_all() so readers cannot race with the array being
> > removed, then free the old array after dropping the lock.
> 
> Out of curiosity: why drop the lock before kfree'ing ?

Because kvfree() can sleep! :)

Thanks,
Wei-Lin Chang

> 
> Thanks!
> Leo
> 
> > 
> > Signed-off-by: Wei-Lin Chang <weilin.chang at arm.com>
> > ---
> >  arch/arm64/kvm/nested.c | 12 ++++++--
> >  arch/arm64/kvm/ptdump.c | 61 ++++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 69 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> > index 6435efd65cb5..17a180ddf6ca 100644
> > --- a/arch/arm64/kvm/nested.c
> > +++ b/arch/arm64/kvm/nested.c
> > @@ -1283,6 +1283,7 @@ void kvm_nested_s2_flush(struct kvm *kvm)
> >  
> >  void kvm_arch_flush_shadow_all(struct kvm *kvm)
> >  {
> > +	struct kvm_s2_mmu *mmus;
> >  	int i;
> >  
> >  	for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
> > @@ -1291,9 +1292,14 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm)
> >  		if (!WARN_ON(atomic_read(&mmu->refcnt)))
> >  			kvm_free_stage2_pgd(mmu);
> >  	}
> > -	kvfree(kvm->arch.nested_mmus);
> > -	kvm->arch.nested_mmus = NULL;
> > -	kvm->arch.nested_mmus_size = 0;
> > +
> > +	scoped_guard(write_lock, &kvm->mmu_lock) {
> > +		mmus = kvm->arch.nested_mmus;
> > +		kvm->arch.nested_mmus = NULL;
> > +		kvm->arch.nested_mmus_size = 0;
> > +	}
> > +
> > +	kvfree(mmus);
> >  	kvm_uninit_stage2_mmu(kvm);
> >  }
> >  
> > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> > index 40f93b7c7ad9..1649eaa75798 100644
> > --- a/arch/arm64/kvm/ptdump.c
> > +++ b/arch/arm64/kvm/ptdump.c
> > @@ -181,6 +181,50 @@ static int kvm_ptdump_guest_canonical_show(struct seq_file *m, void *unused)
> >  	return 0;
> >  }
> >  
> > +static int kvm_ptdump_guest_nested_show(struct seq_file *m, void *unused)
> > +{
> > +	int ret = 0, i;
> > +	struct kvm_ptdump_guest_state *st = m->private;
> > +	struct kvm *kvm = st->kvm;
> > +	struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
> > +		.cb	= kvm_ptdump_visitor,
> > +		.arg	= &st->parser_state,
> > +		.flags	= KVM_PGTABLE_WALK_LEAF,
> > +	};
> > +
> > +	guard(write_lock)(&kvm->mmu_lock);
> > +
> > +	if (!kvm->arch.nested_mmus)
> > +		return 0;
> > +
> > +	for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
> > +		struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
> > +
> > +		if (!mmu->pgt)
> > +			continue;
> > +
> > +		if (kvm_s2_mmu_valid(mmu)) {
> > +			memset(st, 0, sizeof(*st));
> > +			ret = kvm_ptdump_parser_init(st, kvm, mmu->pgt);
> > +			if (ret)
> > +				return ret;
> > +			st->parser_state = (struct ptdump_pg_state) {
> > +				.marker		= &st->ipa_marker[0],
> > +				.level		= -1,
> > +				.pg_level	= &st->level[0],
> > +				.seq		= m,
> > +			};
> > +			seq_printf(m, "nested mmu %d VTCR: 0x%016llx VTTBR: 0x%016llx s2: %s\n",
> > +				   i, mmu->tlb_vtcr, mmu->tlb_vttbr,
> > +				   mmu->nested_stage2_enabled ? "enabled" : "disabled");
> > +			ret = kvm_pgtable_walk(mmu->pgt, 0, BIT(mmu->pgt->ia_bits), &walker);
> > +			if (ret)
> > +				return ret;
> > +		}
> > +	}
> > +	return ret;
> > +}
> > +
> >  static int kvm_ptdump_guest_open(struct inode *m, struct file *file,
> >  				 int (*show)(struct seq_file *, void *))
> >  {
> > @@ -212,6 +256,11 @@ static int kvm_ptdump_guest_canonical_open(struct inode *m, struct file *file)
> >  	return kvm_ptdump_guest_open(m, file, kvm_ptdump_guest_canonical_show);
> >  }
> >  
> > +static int kvm_ptdump_guest_nested_open(struct inode *m, struct file *file)
> > +{
> > +	return kvm_ptdump_guest_open(m, file, kvm_ptdump_guest_nested_show);
> > +}
> > +
> >  static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
> >  {
> >  	struct kvm *kvm = m->i_private;
> > @@ -230,6 +279,13 @@ static const struct file_operations kvm_ptdump_guest_canonical_fops = {
> >  	.release	= kvm_ptdump_guest_close,
> >  };
> >  
> > +static const struct file_operations kvm_ptdump_guest_nested_fops = {
> > +	.open		= kvm_ptdump_guest_nested_open,
> > +	.read		= seq_read,
> > +	.llseek		= seq_lseek,
> > +	.release	= kvm_ptdump_guest_close,
> > +};
> > +
> >  static int kvm_pgtable_range_show(struct seq_file *m, void *unused)
> >  {
> >  	struct kvm *kvm = m->private;
> > @@ -307,6 +363,9 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
> >  			    kvm, &kvm_pgtable_range_fops);
> >  	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
> >  			    kvm, &kvm_pgtable_levels_fops);
> > -	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
> > +	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT)) {
> >  		kvm->arch.debugfs_nv_dentry = debugfs_create_dir("nested", kvm->debugfs_dentry);
> > +		debugfs_create_file("shadow_page_tables", 0400, kvm->arch.debugfs_nv_dentry,
> > +				    kvm, &kvm_ptdump_guest_nested_fops);
> > +	}
> >  }
> > -- 
> > 2.43.0
> >