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

[Itaru Kitayama <itaru.kitayama@fujitsu.com>]

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.
> 
> Signed-off-by: Wei-Lin Chang <weilin.chang@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");

This header information in the debugfs "shadow_page_tables" file, under
the nested directory is showing guest hypervisor's configuration while
the file is designed to show nested guest's shadwo stage 2 translation
tables layouts owned by Host EL2 hypervisor. Is this intentional?

Thanks,
Itaru.

> +			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
>