Re: [PATCH v3 1/2] arm64: ptdump: Make note_page_flush() range aware

[Marc Zyngier]

On Fri, 14 Aug 2026 23:24:57 +0100,
Wei-Lin Chang <weilin.chang@xxxxxxx> wrote:
> 
> note_page_flush() calls note_page() with addr == 0 and level == -1 to
> dump the last row of a ptdump. addr == 0 (1 << 64 wrapped around)
> renders a huge region with enormous size for address spaces with
> IA bits < 64. For example the stage-2 page tables and the EFI runtime
> page table.
> 
> More importantly, the last region of the address space and everything
> after the address space up to 1 << 64 are merged into one row of
> output. If the last region within the address space is valid, it will
> appear to remain valid up to 1 << 64 with the same attributes.
> 
> Currently only the EFI runtime ptdump is affected by this, but KVM will
> soon fix its stage-2 ptdump by using note_page_flush(). Here is an
> example of an EFI runtime ptdump (last row):
> 
> 0x0000008000000000-0x0000000000000000   17179868672G PGD
> 
> With this patch:
> 
> 0x0000008000000000-0x0001000000000000      261632G PGD
> 
> To fix this, cache the end address of a ptdump in ptdump_pg_state so
> note_page_flush() can call the final note_page() with the correct end
> address.
> 
> Fixes: 9d80448ac92b ("efi/arm64: Add debugfs node to dump UEFI runtime page tables")
> Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> ---
>  arch/arm64/include/asm/ptdump.h |  2 ++
>  arch/arm64/mm/ptdump.c          | 14 +++++++++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
> index 5b374a6ab34a..1b743de7d89e 100644
> --- a/arch/arm64/include/asm/ptdump.h
> +++ b/arch/arm64/include/asm/ptdump.h
> @@ -52,6 +52,8 @@ struct ptdump_pg_state {
>  	const struct addr_marker *marker;
>  	const struct mm_struct *mm;
>  	unsigned long start_address;
> +	/* exclusive end, ULONG_MAX represents an end at 1 << 64 */
> +	unsigned long end_address;
>  	int level;
>  	ptval_t current_prot;
>  	bool check_wx;
> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> index 1c20144700d7..eab400e744d9 100644
> --- a/arch/arm64/mm/ptdump.c
> +++ b/arch/arm64/mm/ptdump.c
> @@ -278,9 +278,19 @@ void note_page_pgd(struct ptdump_state *pt_st, unsigned long addr, pgd_t pgd)
>  
>  void note_page_flush(struct ptdump_state *pt_st)
>  {
> +	struct ptdump_pg_state *st = container_of(pt_st, struct ptdump_pg_state, ptdump);
> +	unsigned long end = st->end_address;
>  	pte_t pte_zero = {0};
>  
> -	note_page(pt_st, 0, -1, pte_val(pte_zero));
> +	/*
> +	 * Address spaces that end at 1 << 64 have end_address == ULONG_MAX,
> +	 * but note_page() expects the exclusive end. In this case adjust end
> +	 * to the wraparound value 0.
> +	 */
> +	if (end == ULONG_MAX)
> +		end = 0;
> +
> +	note_page(pt_st, end, -1, pte_val(pte_zero));
>  }
>  
>  static void arm64_ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
> @@ -303,6 +313,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
>  		.marker = info->markers,
>  		.mm = info->mm,
>  		.pg_level = &kernel_pg_levels[0],
> +		.end_address = end,
>  		.level = -1,
>  		.ptdump = {
>  			.note_page_pte = note_page_pte,
> @@ -344,6 +355,7 @@ bool ptdump_check_wx(void)
>  			{ -1, NULL},
>  		},
>  		.pg_level = &kernel_pg_levels[0],
> +		.end_address = ~0UL,

nit: shouldn't this be ULONG_MAX instead? Yes, this is the same thing,
but it doesn't hurt to match the documentation.

Thanks,

	M.

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