[PATCH RESEND 0/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[PATCH RESEND 0/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

[sorry for the resend, I generated the cover letter with the wrong
commits previously, I should automate this :P]

Hi,

This series exposes shadow page tables in debugfs to improve the
debugability and testability of NV. First we teach the KVM ptdump code
to handle different s2 mmus, then shadow page tables are exposed. This
is gated also behind CONFIG_PTDUMP_STAGE2_DEBUGFS, like the canonical
stage-2 page table.

The file names for the shadow page tables are formatted
0x<vttbr>-0x<vtcr>-s2-{en,dis}abled, which is the most intuitive way of
identifying the s2 mmus but not terribly clear. For now I don't think of
other options that are meaningfully better, any suggestion welcome.

I realized I tend to write long variable and function names, happy to
change if anyone finds it too verbose.

Thanks!


Wei-Lin Chang (2):
  KVM: arm64: ptdump: Make KVM ptdump code s2 mmu aware
  KVM: arm64: nv: Expose shadow page tables in debugfs

 arch/arm64/include/asm/kvm_host.h |  7 ++++
 arch/arm64/include/asm/kvm_mmu.h  |  4 +++
 arch/arm64/kvm/nested.c           |  6 +++-
 arch/arm64/kvm/ptdump.c           | 60 ++++++++++++++++++++++---------
 4 files changed, 60 insertions(+), 17 deletions(-)

-- 
2.43.0

[PATCH RESEND 1/2] KVM: arm64: ptdump: Make KVM ptdump code s2 mmu aware

[Wei-Lin Chang]

To reuse the ptdump code for shadow page table dumping later, let's pass
s2 mmu as the private data, so we have the freedom to select which page
table to print.

Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
---
 arch/arm64/kvm/ptdump.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
index 6cbe018fd6fd..98763b291956 100644
--- a/arch/arm64/kvm/ptdump.c
+++ b/arch/arm64/kvm/ptdump.c
@@ -18,7 +18,7 @@
 #define KVM_PGTABLE_MAX_LEVELS	(KVM_PGTABLE_LAST_LEVEL + 1)
 
 struct kvm_ptdump_guest_state {
-	struct kvm		*kvm;
+	struct kvm_s2_mmu	*mmu;
 	struct ptdump_pg_state	parser_state;
 	struct addr_marker	ipa_marker[MARKERS_LEN];
 	struct ptdump_pg_level	level[KVM_PGTABLE_MAX_LEVELS];
@@ -112,10 +112,9 @@ static int kvm_ptdump_build_levels(struct ptdump_pg_level *level, u32 start_lvl)
 	return 0;
 }
 
-static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm *kvm)
+static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm_s2_mmu *mmu)
 {
 	struct kvm_ptdump_guest_state *st;
-	struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
 	struct kvm_pgtable *pgtable = mmu->pgt;
 	int ret;
 
@@ -133,7 +132,7 @@ static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm *kvm)
 	st->ipa_marker[1].start_address = BIT(pgtable->ia_bits);
 	st->range[0].end		= BIT(pgtable->ia_bits);
 
-	st->kvm				= kvm;
+	st->mmu				= mmu;
 	st->parser_state = (struct ptdump_pg_state) {
 		.marker		= &st->ipa_marker[0],
 		.level		= -1,
@@ -149,8 +148,8 @@ static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
 {
 	int ret;
 	struct kvm_ptdump_guest_state *st = m->private;
-	struct kvm *kvm = st->kvm;
-	struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
+	struct kvm_s2_mmu *mmu = st->mmu;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
 	struct ptdump_pg_state *parser_state = &st->parser_state;
 	struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
 		.cb	= kvm_ptdump_visitor,
@@ -169,14 +168,15 @@ static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
 
 static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
 {
-	struct kvm *kvm = m->i_private;
+	struct kvm_s2_mmu *mmu = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
 	struct kvm_ptdump_guest_state *st;
 	int ret;
 
 	if (!kvm_get_kvm_safe(kvm))
 		return -ENOENT;
 
-	st = kvm_ptdump_parser_create(kvm);
+	st = kvm_ptdump_parser_create(mmu);
 	if (IS_ERR(st)) {
 		ret = PTR_ERR(st);
 		goto err_with_kvm_ref;
@@ -194,7 +194,7 @@ static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
 
 static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
 {
-	struct kvm *kvm = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(m->i_private);
 	void *st = ((struct seq_file *)file->private_data)->private;
 
 	kfree(st);
@@ -229,14 +229,15 @@ static int kvm_pgtable_levels_show(struct seq_file *m, void *unused)
 static int kvm_pgtable_debugfs_open(struct inode *m, struct file *file,
 				    int (*show)(struct seq_file *, void *))
 {
-	struct kvm *kvm = m->i_private;
+	struct kvm_s2_mmu *mmu = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
 	struct kvm_pgtable *pgtable;
 	int ret;
 
 	if (!kvm_get_kvm_safe(kvm))
 		return -ENOENT;
 
-	pgtable = kvm->arch.mmu.pgt;
+	pgtable = mmu->pgt;
 
 	ret = single_open(file, show, pgtable);
 	if (ret < 0)
@@ -256,7 +257,7 @@ static int kvm_pgtable_levels_open(struct inode *m, struct file *file)
 
 static int kvm_pgtable_debugfs_close(struct inode *m, struct file *file)
 {
-	struct kvm *kvm = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(m->i_private);
 
 	kvm_put_kvm(kvm);
 	return single_release(m, file);
@@ -279,9 +280,9 @@ static const struct file_operations kvm_pgtable_levels_fops = {
 void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
 {
 	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
-			    kvm, &kvm_ptdump_guest_fops);
-	debugfs_create_file("ipa_range", 0400, kvm->debugfs_dentry, kvm,
-			    &kvm_pgtable_range_fops);
+			    &kvm->arch.mmu, &kvm_ptdump_guest_fops);
+	debugfs_create_file("ipa_range", 0400, kvm->debugfs_dentry,
+			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
 	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
-			    kvm, &kvm_pgtable_levels_fops);
+			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
 }
-- 
2.43.0

[PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

Exposing shadow page tables in debugfs improves the debugability and
testability of NV. With this patch a new directory "nested" is created
for each VM created if the host is NV capable. Within the directory each
valid s2 mmu will have its shadow page table exposed as a readable file
with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
creation and removal of the files happen at the points when an s2 mmu
becomes valid, or the context it represents change. In the future the
"nested" directory can also hold other NV related information.

This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
---
 arch/arm64/include/asm/kvm_host.h |  7 +++++++
 arch/arm64/include/asm/kvm_mmu.h  |  4 ++++
 arch/arm64/kvm/nested.c           |  6 +++++-
 arch/arm64/kvm/ptdump.c           | 27 +++++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 5d5a3bbdb95e..f88f6c4d646e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -217,6 +217,10 @@ struct kvm_s2_mmu {
 	 */
 	bool	nested_stage2_enabled;
 
+#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
+	struct dentry *shadow_pt_debugfs_dentry;
+#endif
+
 	/*
 	 * true when this MMU needs to be unmapped before being used for a new
 	 * purpose.
@@ -405,6 +409,9 @@ struct kvm_arch {
 	 * the associated pKVM instance in the hypervisor.
 	 */
 	struct kvm_protected_vm pkvm;
+
+	/* Nested virtualization info */
+	struct dentry *debugfs_nv_dentry;
 };
 
 struct kvm_vcpu_fault_info {
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index d968aca0461a..01e9c72d6aa7 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
 
 #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
 void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
+void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
+void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
 #else
 static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
+static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
+static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
 #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
 
 #endif /* __ASSEMBLER__ */
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index eeea5e692370..31d74ed8449e 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -730,8 +730,10 @@ 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))
+	if (kvm_s2_mmu_valid(s2_mmu)) {
+		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
 		s2_mmu->pending_unmap = true;
+	}
 
 	/*
 	 * The virtual VMID (modulo CnP) will be used as a key when matching
@@ -745,6 +747,8 @@ 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);
 
diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
index 98763b291956..3a70f633fc8b 100644
--- a/arch/arm64/kvm/ptdump.c
+++ b/arch/arm64/kvm/ptdump.c
@@ -10,6 +10,7 @@
 #include <linux/kvm_host.h>
 #include <linux/seq_file.h>
 
+#include <asm/cpufeature.h>
 #include <asm/kvm_mmu.h>
 #include <asm/kvm_pgtable.h>
 #include <asm/ptdump.h>
@@ -277,6 +278,29 @@ static const struct file_operations kvm_pgtable_levels_fops = {
 	.release	= kvm_pgtable_debugfs_close,
 };
 
+void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
+{
+	struct dentry *dent;
+	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
+	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
+
+	snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled",
+		 mmu->tlb_vttbr,
+		 mmu->tlb_vtcr,
+		 mmu->nested_stage2_enabled ? "en" : "dis");
+
+	dent = debugfs_create_file(file_name, 0400,
+				   mmu->arch->debugfs_nv_dentry, mmu,
+				   &kvm_ptdump_guest_fops);
+
+	mmu->shadow_pt_debugfs_dentry = dent;
+}
+
+void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
+{
+	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
+}
+
 void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
 {
 	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
@@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
 			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
 	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
 			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
+	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
+		kvm->arch.debugfs_nv_dentry =
+			debugfs_create_dir("nested", kvm->debugfs_dentry);
 }
-- 
2.43.0

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Joey Gouly]

On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:
> Exposing shadow page tables in debugfs improves the debugability and
> testability of NV. With this patch a new directory "nested" is created
> for each VM created if the host is NV capable. Within the directory each
> valid s2 mmu will have its shadow page table exposed as a readable file
> with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
> creation and removal of the files happen at the points when an s2 mmu
> becomes valid, or the context it represents change. In the future the
> "nested" directory can also hold other NV related information.
> 
> This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.
> 
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  7 +++++++
>  arch/arm64/include/asm/kvm_mmu.h  |  4 ++++
>  arch/arm64/kvm/nested.c           |  6 +++++-
>  arch/arm64/kvm/ptdump.c           | 27 +++++++++++++++++++++++++++
>  4 files changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5d5a3bbdb95e..f88f6c4d646e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
>  	 */
>  	bool	nested_stage2_enabled;
>  
> +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> +	struct dentry *shadow_pt_debugfs_dentry;
> +#endif
> +
>  	/*
>  	 * true when this MMU needs to be unmapped before being used for a new
>  	 * purpose.
> @@ -405,6 +409,9 @@ struct kvm_arch {
>  	 * the associated pKVM instance in the hypervisor.
>  	 */
>  	struct kvm_protected_vm pkvm;
> +
> +	/* Nested virtualization info */
> +	struct dentry *debugfs_nv_dentry;

Seems like this could be guarded with CONFIG_PTDUMP_STAGE2_DEBUGFS too, or is
there a reason you didn't?

Thanks,
Joey

>  };
>  
>  struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index d968aca0461a..01e9c72d6aa7 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
>  
>  #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
>  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
> +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
> +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
>  #else
>  static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
> +static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
> +static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
>  #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
>  
>  #endif /* __ASSEMBLER__ */
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index eeea5e692370..31d74ed8449e 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -730,8 +730,10 @@ 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))
> +	if (kvm_s2_mmu_valid(s2_mmu)) {
> +		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
>  		s2_mmu->pending_unmap = true;
> +	}
>  
>  	/*
>  	 * The virtual VMID (modulo CnP) will be used as a key when matching
> @@ -745,6 +747,8 @@ 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);
>  
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> index 98763b291956..3a70f633fc8b 100644
> --- a/arch/arm64/kvm/ptdump.c
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -10,6 +10,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/seq_file.h>
>  
> +#include <asm/cpufeature.h>
>  #include <asm/kvm_mmu.h>
>  #include <asm/kvm_pgtable.h>
>  #include <asm/ptdump.h>
> @@ -277,6 +278,29 @@ static const struct file_operations kvm_pgtable_levels_fops = {
>  	.release	= kvm_pgtable_debugfs_close,
>  };
>  
> +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> +{
> +	struct dentry *dent;
> +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
> +
> +	snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled",
> +		 mmu->tlb_vttbr,
> +		 mmu->tlb_vtcr,
> +		 mmu->nested_stage2_enabled ? "en" : "dis");
> +
> +	dent = debugfs_create_file(file_name, 0400,
> +				   mmu->arch->debugfs_nv_dentry, mmu,
> +				   &kvm_ptdump_guest_fops);
> +
> +	mmu->shadow_pt_debugfs_dentry = dent;
> +}
> +
> +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
> +{
> +	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
> +}
> +
>  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
>  {
>  	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
> @@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
>  			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
>  	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
>  			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
> +	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
> +		kvm->arch.debugfs_nv_dentry =
> +			debugfs_create_dir("nested", kvm->debugfs_dentry);
>  }
> -- 
> 2.43.0
> 

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

On Tue, Mar 10, 2026 at 03:26:04PM +0000, Joey Gouly wrote:
> On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:
> > Exposing shadow page tables in debugfs improves the debugability and
> > testability of NV. With this patch a new directory "nested" is created
> > for each VM created if the host is NV capable. Within the directory each
> > valid s2 mmu will have its shadow page table exposed as a readable file
> > with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
> > creation and removal of the files happen at the points when an s2 mmu
> > becomes valid, or the context it represents change. In the future the
> > "nested" directory can also hold other NV related information.
> > 
> > This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.
> > 
> > Suggested-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
> > ---
> >  arch/arm64/include/asm/kvm_host.h |  7 +++++++
> >  arch/arm64/include/asm/kvm_mmu.h  |  4 ++++
> >  arch/arm64/kvm/nested.c           |  6 +++++-
> >  arch/arm64/kvm/ptdump.c           | 27 +++++++++++++++++++++++++++
> >  4 files changed, 43 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 5d5a3bbdb95e..f88f6c4d646e 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
> >  	 */
> >  	bool	nested_stage2_enabled;
> >  
> > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> > +	struct dentry *shadow_pt_debugfs_dentry;
> > +#endif
> > +
> >  	/*
> >  	 * true when this MMU needs to be unmapped before being used for a new
> >  	 * purpose.
> > @@ -405,6 +409,9 @@ struct kvm_arch {
> >  	 * the associated pKVM instance in the hypervisor.
> >  	 */
> >  	struct kvm_protected_vm pkvm;
> > +
> > +	/* Nested virtualization info */
> > +	struct dentry *debugfs_nv_dentry;
> 
> Seems like this could be guarded with CONFIG_PTDUMP_STAGE2_DEBUGFS too, or is
> there a reason you didn't?

Right, I was thinking this "nested" directory can also hold other NV
related information in the future, that's why I didn't keep it behind
the option.

Thanks,
Wei-Lin Chang

> 
> Thanks,
> Joey
> 
> >  };
> >  
> >  struct kvm_vcpu_fault_info {
> > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> > index d968aca0461a..01e9c72d6aa7 100644
> > --- a/arch/arm64/include/asm/kvm_mmu.h
> > +++ b/arch/arm64/include/asm/kvm_mmu.h
> > @@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
> >  
> >  #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> >  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
> > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
> > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
> >  #else
> >  static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
> > +static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
> > +static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
> >  #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
> >  
> >  #endif /* __ASSEMBLER__ */
> > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> > index eeea5e692370..31d74ed8449e 100644
> > --- a/arch/arm64/kvm/nested.c
> > +++ b/arch/arm64/kvm/nested.c
> > @@ -730,8 +730,10 @@ 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))
> > +	if (kvm_s2_mmu_valid(s2_mmu)) {
> > +		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
> >  		s2_mmu->pending_unmap = true;
> > +	}
> >  
> >  	/*
> >  	 * The virtual VMID (modulo CnP) will be used as a key when matching
> > @@ -745,6 +747,8 @@ 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);
> >  
> > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> > index 98763b291956..3a70f633fc8b 100644
> > --- a/arch/arm64/kvm/ptdump.c
> > +++ b/arch/arm64/kvm/ptdump.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/kvm_host.h>
> >  #include <linux/seq_file.h>
> >  
> > +#include <asm/cpufeature.h>
> >  #include <asm/kvm_mmu.h>
> >  #include <asm/kvm_pgtable.h>
> >  #include <asm/ptdump.h>
> > @@ -277,6 +278,29 @@ static const struct file_operations kvm_pgtable_levels_fops = {
> >  	.release	= kvm_pgtable_debugfs_close,
> >  };
> >  
> > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> > +{
> > +	struct dentry *dent;
> > +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> > +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
> > +
> > +	snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled",
> > +		 mmu->tlb_vttbr,
> > +		 mmu->tlb_vtcr,
> > +		 mmu->nested_stage2_enabled ? "en" : "dis");
> > +
> > +	dent = debugfs_create_file(file_name, 0400,
> > +				   mmu->arch->debugfs_nv_dentry, mmu,
> > +				   &kvm_ptdump_guest_fops);
> > +
> > +	mmu->shadow_pt_debugfs_dentry = dent;
> > +}
> > +
> > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
> > +{
> > +	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
> > +}
> > +
> >  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
> >  {
> >  	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
> > @@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
> >  			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
> >  	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
> >  			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
> > +	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
> > +		kvm->arch.debugfs_nv_dentry =
> > +			debugfs_create_dir("nested", kvm->debugfs_dentry);
> >  }
> > -- 
> > 2.43.0
> > 

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Marc Zyngier]

On Tue, 10 Mar 2026 16:17:07 +0000,
Wei-Lin Chang <weilin.chang@arm.com> wrote:
> 
> On Tue, Mar 10, 2026 at 03:26:04PM +0000, Joey Gouly wrote:

> > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > > index 5d5a3bbdb95e..f88f6c4d646e 100644
> > > --- a/arch/arm64/include/asm/kvm_host.h
> > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
> > >  	 */
> > >  	bool	nested_stage2_enabled;
> > >  
> > > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> > > +	struct dentry *shadow_pt_debugfs_dentry;
> > > +#endif
> > > +
> > >  	/*
> > >  	 * true when this MMU needs to be unmapped before being used for a new
> > >  	 * purpose.
> > > @@ -405,6 +409,9 @@ struct kvm_arch {
> > >  	 * the associated pKVM instance in the hypervisor.
> > >  	 */
> > >  	struct kvm_protected_vm pkvm;
> > > +
> > > +	/* Nested virtualization info */
> > > +	struct dentry *debugfs_nv_dentry;
> > 
> > Seems like this could be guarded with CONFIG_PTDUMP_STAGE2_DEBUGFS too, or is
> > there a reason you didn't?
> 
> Right, I was thinking this "nested" directory can also hold other NV
> related information in the future, that's why I didn't keep it behind
> the option.

We can cross that bridge when we get there. In the meantime, I'd side
with Joey and would rather not have a dangling pointer.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

On Tue, Mar 10, 2026 at 04:50:22PM +0000, Marc Zyngier wrote:
> On Tue, 10 Mar 2026 16:17:07 +0000,
> Wei-Lin Chang <weilin.chang@arm.com> wrote:
> > 
> > On Tue, Mar 10, 2026 at 03:26:04PM +0000, Joey Gouly wrote:
> 
> > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > > > index 5d5a3bbdb95e..f88f6c4d646e 100644
> > > > --- a/arch/arm64/include/asm/kvm_host.h
> > > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > > @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
> > > >  	 */
> > > >  	bool	nested_stage2_enabled;
> > > >  
> > > > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> > > > +	struct dentry *shadow_pt_debugfs_dentry;
> > > > +#endif
> > > > +
> > > >  	/*
> > > >  	 * true when this MMU needs to be unmapped before being used for a new
> > > >  	 * purpose.
> > > > @@ -405,6 +409,9 @@ struct kvm_arch {
> > > >  	 * the associated pKVM instance in the hypervisor.
> > > >  	 */
> > > >  	struct kvm_protected_vm pkvm;
> > > > +
> > > > +	/* Nested virtualization info */
> > > > +	struct dentry *debugfs_nv_dentry;
> > > 
> > > Seems like this could be guarded with CONFIG_PTDUMP_STAGE2_DEBUGFS too, or is
> > > there a reason you didn't?
> > 
> > Right, I was thinking this "nested" directory can also hold other NV
> > related information in the future, that's why I didn't keep it behind
> > the option.
> 
> We can cross that bridge when we get there. In the meantime, I'd side
> with Joey and would rather not have a dangling pointer.

Sure!
Let me guard it with CONFIG_PTDUMP_STAGE2_DEBUGFS too.

Thanks,
Wei-Lin Chang

> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Sebastian Ene]

On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:
> Exposing shadow page tables in debugfs improves the debugability and
> testability of NV. With this patch a new directory "nested" is created
> for each VM created if the host is NV capable. Within the directory each
> valid s2 mmu will have its shadow page table exposed as a readable file
> with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
> creation and removal of the files happen at the points when an s2 mmu
> becomes valid, or the context it represents change. In the future the
> "nested" directory can also hold other NV related information.
> 
> This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.
> 
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  7 +++++++
>  arch/arm64/include/asm/kvm_mmu.h  |  4 ++++
>  arch/arm64/kvm/nested.c           |  6 +++++-
>  arch/arm64/kvm/ptdump.c           | 27 +++++++++++++++++++++++++++
>  4 files changed, 43 insertions(+), 1 deletion(-)

Hi,

> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5d5a3bbdb95e..f88f6c4d646e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
>  	 */
>  	bool	nested_stage2_enabled;
>  
> +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> +	struct dentry *shadow_pt_debugfs_dentry;
> +#endif
> +
>  	/*
>  	 * true when this MMU needs to be unmapped before being used for a new
>  	 * purpose.
> @@ -405,6 +409,9 @@ struct kvm_arch {
>  	 * the associated pKVM instance in the hypervisor.
>  	 */
>  	struct kvm_protected_vm pkvm;
> +
> +	/* Nested virtualization info */
> +	struct dentry *debugfs_nv_dentry;
>  };
>  
>  struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index d968aca0461a..01e9c72d6aa7 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
>  
>  #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
>  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
> +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
> +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
>  #else
>  static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
> +static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
> +static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
>  #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
>  
>  #endif /* __ASSEMBLER__ */
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index eeea5e692370..31d74ed8449e 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -730,8 +730,10 @@ 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))
> +	if (kvm_s2_mmu_valid(s2_mmu)) {
> +		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
>  		s2_mmu->pending_unmap = true;
> +	}
>  
>  	/*
>  	 * The virtual VMID (modulo CnP) will be used as a key when matching
> @@ -745,6 +747,8 @@ 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);
>  
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> index 98763b291956..3a70f633fc8b 100644
> --- a/arch/arm64/kvm/ptdump.c
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -10,6 +10,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/seq_file.h>
>  
> +#include <asm/cpufeature.h>
>  #include <asm/kvm_mmu.h>
>  #include <asm/kvm_pgtable.h>
>  #include <asm/ptdump.h>
> @@ -277,6 +278,29 @@ static const struct file_operations kvm_pgtable_levels_fops = {
>  	.release	= kvm_pgtable_debugfs_close,
>  };
>  
> +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> +{
> +	struct dentry *dent;
> +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];

Can you hide the size of this definition behind a macro ?

> +
> +	snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled",
> +		 mmu->tlb_vttbr,
> +		 mmu->tlb_vtcr,
> +		 mmu->nested_stage2_enabled ? "en" : "dis");
> +
> +	dent = debugfs_create_file(file_name, 0400,
> +				   mmu->arch->debugfs_nv_dentry, mmu,
> +				   &kvm_ptdump_guest_fops);
> +
> +	mmu->shadow_pt_debugfs_dentry = dent;
> +}
> +
> +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
> +{
> +	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
> +}
> +
>  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
>  {
>  	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
> @@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
>  			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
>  	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
>  			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
> +	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
> +		kvm->arch.debugfs_nv_dentry =
> +			debugfs_create_dir("nested", kvm->debugfs_dentry);
>  }

Other than that this looks good to me, thanks
Reviewed-by: Sebastian Ene <sebastianene@google.com>

> -- 
> 2.43.0
> 

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

On Wed, Mar 11, 2026 at 03:41:32PM +0000, Sebastian Ene wrote:
> On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:
> > Exposing shadow page tables in debugfs improves the debugability and
> > testability of NV. With this patch a new directory "nested" is created
> > for each VM created if the host is NV capable. Within the directory each
> > valid s2 mmu will have its shadow page table exposed as a readable file
> > with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
> > creation and removal of the files happen at the points when an s2 mmu
> > becomes valid, or the context it represents change. In the future the
> > "nested" directory can also hold other NV related information.
> > 
> > This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.
> > 
> > Suggested-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
> > ---
> >  arch/arm64/include/asm/kvm_host.h |  7 +++++++
> >  arch/arm64/include/asm/kvm_mmu.h  |  4 ++++
> >  arch/arm64/kvm/nested.c           |  6 +++++-
> >  arch/arm64/kvm/ptdump.c           | 27 +++++++++++++++++++++++++++
> >  4 files changed, 43 insertions(+), 1 deletion(-)
> 
> Hi,
> 
> > 
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 5d5a3bbdb95e..f88f6c4d646e 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -217,6 +217,10 @@ struct kvm_s2_mmu {
> >  	 */
> >  	bool	nested_stage2_enabled;
> >  
> > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> > +	struct dentry *shadow_pt_debugfs_dentry;
> > +#endif
> > +
> >  	/*
> >  	 * true when this MMU needs to be unmapped before being used for a new
> >  	 * purpose.
> > @@ -405,6 +409,9 @@ struct kvm_arch {
> >  	 * the associated pKVM instance in the hypervisor.
> >  	 */
> >  	struct kvm_protected_vm pkvm;
> > +
> > +	/* Nested virtualization info */
> > +	struct dentry *debugfs_nv_dentry;
> >  };
> >  
> >  struct kvm_vcpu_fault_info {
> > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> > index d968aca0461a..01e9c72d6aa7 100644
> > --- a/arch/arm64/include/asm/kvm_mmu.h
> > +++ b/arch/arm64/include/asm/kvm_mmu.h
> > @@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
> >  
> >  #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> >  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
> > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
> > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
> >  #else
> >  static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
> > +static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
> > +static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
> >  #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
> >  
> >  #endif /* __ASSEMBLER__ */
> > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> > index eeea5e692370..31d74ed8449e 100644
> > --- a/arch/arm64/kvm/nested.c
> > +++ b/arch/arm64/kvm/nested.c
> > @@ -730,8 +730,10 @@ 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))
> > +	if (kvm_s2_mmu_valid(s2_mmu)) {
> > +		kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
> >  		s2_mmu->pending_unmap = true;
> > +	}
> >  
> >  	/*
> >  	 * The virtual VMID (modulo CnP) will be used as a key when matching
> > @@ -745,6 +747,8 @@ 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);
> >  
> > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> > index 98763b291956..3a70f633fc8b 100644
> > --- a/arch/arm64/kvm/ptdump.c
> > +++ b/arch/arm64/kvm/ptdump.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/kvm_host.h>
> >  #include <linux/seq_file.h>
> >  
> > +#include <asm/cpufeature.h>
> >  #include <asm/kvm_mmu.h>
> >  #include <asm/kvm_pgtable.h>
> >  #include <asm/ptdump.h>
> > @@ -277,6 +278,29 @@ static const struct file_operations kvm_pgtable_levels_fops = {
> >  	.release	= kvm_pgtable_debugfs_close,
> >  };
> >  
> > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> > +{
> > +	struct dentry *dent;
> > +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> > +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
> 
> Can you hide the size of this definition behind a macro ?

Sure, no problem.

> 
> > +
> > +	snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled",
> > +		 mmu->tlb_vttbr,
> > +		 mmu->tlb_vtcr,
> > +		 mmu->nested_stage2_enabled ? "en" : "dis");
> > +
> > +	dent = debugfs_create_file(file_name, 0400,
> > +				   mmu->arch->debugfs_nv_dentry, mmu,
> > +				   &kvm_ptdump_guest_fops);
> > +
> > +	mmu->shadow_pt_debugfs_dentry = dent;
> > +}
> > +
> > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
> > +{
> > +	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
> > +}
> > +
> >  void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
> >  {
> >  	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
> > @@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
> >  			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
> >  	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
> >  			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
> > +	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
> > +		kvm->arch.debugfs_nv_dentry =
> > +			debugfs_create_dir("nested", kvm->debugfs_dentry);
> >  }
> 
> Other than that this looks good to me, thanks
> Reviewed-by: Sebastian Ene <sebastianene@google.com>

Thanks for the review!

Thanks,
Wei-Lin Chang
> 
> > -- 
> > 2.43.0
> > 

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Marc Zyngier]

On Fri, 13 Mar 2026 22:28:38 +0000,
Wei-Lin Chang <weilin.chang@arm.com> wrote:
> 
> On Wed, Mar 11, 2026 at 03:41:32PM +0000, Sebastian Ene wrote:
> > On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:

[...]

> > > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> > > +{
> > > +	struct dentry *dent;
> > > +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> > > +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
> > 
> > Can you hide the size of this definition behind a macro ?
> 
> Sure, no problem.

I don't think a macro helps that much on its own. I'd rather this is
made a bit more foolproof by directly expressing the actual string
this results into, and use that for the size:

  #define S2FNAMESZ sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled")

  char file_name[S2FNAME];

which is less ambiguous. The compiler will happily optimise this to a
nice constant that also accounts for the final '\0'.

Thanks,

	M.

-- 
Jazz isn't dead. It just smells funny.

Re: [PATCH RESEND 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs

[Wei-Lin Chang]

On Sat, Mar 14, 2026 at 09:39:17AM +0000, Marc Zyngier wrote:
> On Fri, 13 Mar 2026 22:28:38 +0000,
> Wei-Lin Chang <weilin.chang@arm.com> wrote:
> > 
> > On Wed, Mar 11, 2026 at 03:41:32PM +0000, Sebastian Ene wrote:
> > > On Sun, Mar 08, 2026 at 11:18:29PM +0000, Wei-Lin Chang wrote:
> 
> [...]
> 
> > > > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
> > > > +{
> > > > +	struct dentry *dent;
> > > > +	/* format: 0x<vttbr>-0x<vtcr>-s2-{en, dis}abled\0 */
> > > > +	char file_name[2 + 16 + 1 + 2 + 16 + 4 + 3 + 6];
> > > 
> > > Can you hide the size of this definition behind a macro ?
> > 
> > Sure, no problem.
> 
> I don't think a macro helps that much on its own. I'd rather this is
> made a bit more foolproof by directly expressing the actual string
> this results into, and use that for the size:
> 
>   #define S2FNAMESZ sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled")
> 
>   char file_name[S2FNAME];
> 
> which is less ambiguous. The compiler will happily optimise this to a
> nice constant that also accounts for the final '\0'.

Thanks for the advice!
Makes sense to me, I'll change it to that.

Thanks,
Wei-Lin Chang

> 
> Thanks,
> 
> 	M.
> 
> -- 
> Jazz isn't dead. It just smells funny.