Re: [PATCH] KVM: arm64: ptdump: Flush the last region

[Mark Rutland]

On Sat, Jul 18, 2026 at 12:12:33AM +0100, Wei-Lin Chang wrote:
> Currently the stage-2 ptdump calls note_page() at each leaf entry visit.
> This simply misses the output of the last region, because note_page()
> only dumps output when it detects a change in level/prot, or when the
> walk enters a next marker section. The last region in the guest IPA
> space with the same level/prot is not dumped since there is no change
> after it.
> 
> To dump the final region, manually issue a note_page() call with address
> BIT(ia_bits) (end of guest IPA space) and level == -1 to trigger a level
> change after the last region. Additionally treat level == -1 as a last
> flushing note_page() call and avoid dumping the name of the next marker
> for this case.

I think you can use note_page_flush() rather than doing that manually.

> Fixes: 7c4f73548ed1 ("KVM: arm64: Register ptdump with debugfs on guest creation")
> Reported-by: Sashiko AI <sashiko-bot@xxxxxxxxxx>
> Closes: https://lore.kernel.org/kvmarm/20260630122758.891011F00A3A@xxxxxxxxxxxxxxx/
> Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> ---
>  arch/arm64/kvm/ptdump.c | 8 +++++---
>  arch/arm64/mm/ptdump.c  | 5 +++--
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> index c9140e22abcf..4096e4a92fae 100644
> --- a/arch/arm64/kvm/ptdump.c
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -155,11 +155,13 @@ static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
>  		.seq		= m,
>  	};
>  
> -	write_lock(&kvm->mmu_lock);
> +	guard(write_lock)(&kvm->mmu_lock);
>  	ret = kvm_pgtable_walk(mmu->pgt, 0, BIT(mmu->pgt->ia_bits), &walker);
> -	write_unlock(&kvm->mmu_lock);
> +	if (ret)
> +		return ret;
> +	note_page(&st->parser_state.ptdump, BIT(mmu->pgt->ia_bits), -1, 0);

This can be:

	note_page_flush(&st->parser_state.ptdump);

The level change alone should trigger the dump, so the address doesn't
need to be at the end of the guest IPA space.

Importantly, note_page_flush() will pass 0 as the address, which won't
trigger the checks you try to suppress below.

Please use note_page_flush() here, and drop the changes to
arch/arm64/mm/ptdump.c.

>  
> -	return ret;
> +	return 0;
>  }
>  
>  static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> index ab9899ca1e5f..fed4e4407e0e 100644
> --- a/arch/arm64/mm/ptdump.c
> +++ b/arch/arm64/mm/ptdump.c
> @@ -194,6 +194,7 @@ void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
>  	struct ptdump_pg_state *st = container_of(pt_st, struct ptdump_pg_state, ptdump);
>  	struct ptdump_pg_level *pg_level = st->pg_level;
>  	static const char units[] = "KMGTPE";
> +	bool flush = level == -1;
>  	ptdesc_t prot = 0;
>  
>  	/* check if the current level has been folded dynamically */
> @@ -234,7 +235,7 @@ void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
>  				  pg_level[st->level].num);
>  		pt_dump_seq_puts(st->seq, "\n");
>  
> -		if (addr >= st->marker[1].start_address) {
> +		if (addr >= st->marker[1].start_address && !flush) {
>  			st->marker++;
>  			pt_dump_seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
>  		}

If you use note_page_flush(), addr will be 0. As the final marker is at
BIT(pgtable->ia_bits), this condition cannot fire.

> @@ -244,7 +245,7 @@ void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
>  		st->level = level;
>  	}
>  
> -	if (addr >= st->marker[1].start_address) {
> +	if (addr >= st->marker[1].start_address && !flush) {
>  		st->marker++;
>  		pt_dump_seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
>  	}

Likewise here.

Mark.