linux-kernel - Re: [PATCH v8 3/6] arm64: ptdump: Use the mask from the state structure

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Message-ID: <86seuzxq27.wl-maz@kernel.org>
Date: Tue, 20 Aug 2024 14:49:04 +0100
From: Marc Zyngier <maz@...nel.org>
To: Sebastian Ene <sebastianene@...gle.com>
Cc: akpm@...ux-foundation.org,
	alexghiti@...osinc.com,
	ankita@...dia.com,
	ardb@...nel.org,
	catalin.marinas@....com,
	christophe.leroy@...roup.eu,
	james.morse@....com,
	vdonnefort@...gle.com,
	mark.rutland@....com,
	oliver.upton@...ux.dev,
	rananta@...gle.com,
	ryan.roberts@....com,
	shahuang@...hat.com,
	suzuki.poulose@....com,
	will@...nel.org,
	yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...roid.com
Subject: Re: [PATCH v8 3/6] arm64: ptdump: Use the mask from the state structure

On Fri, 16 Aug 2024 13:39:03 +0100,
Sebastian Ene <sebastianene@...gle.com> wrote:
> 
> Printing the descriptor attributes requires accessing a mask which has a
> different set of attributes for stage-2. In preparation for adding support
> for the stage-2 pagetables dumping, use the mask from the local context
> and not from the globally defined pg_level array. Store a pointer to
> the pg_level array in the ptdump state structure. This will allow us to
> extract the mask which is wrapped in the pg_level array and use it for
> descriptor parsing in the note_page.
> 
> Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> ---
>  arch/arm64/include/asm/ptdump.h |  1 +
>  arch/arm64/mm/ptdump.c          | 13 ++++++++-----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
> index bd5d3ee3e8dc..71a7ed01153a 100644
> --- a/arch/arm64/include/asm/ptdump.h
> +++ b/arch/arm64/include/asm/ptdump.h
> @@ -44,6 +44,7 @@ struct ptdump_pg_level {
>   */
>  struct ptdump_pg_state {
>  	struct ptdump_state ptdump;
> +	struct ptdump_pg_level *pg_level;
>  	struct seq_file *seq;
>  	const struct addr_marker *marker;
>  	const struct mm_struct *mm;
> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> index 404751fd30fe..ca53ef274a8b 100644
> --- a/arch/arm64/mm/ptdump.c
> +++ b/arch/arm64/mm/ptdump.c
> @@ -117,7 +117,7 @@ static const struct ptdump_prot_bits pte_bits[] = {
>  	}
>  };
>  
> -static struct ptdump_pg_level pg_level[] __ro_after_init = {
> +static struct ptdump_pg_level kernel_pg_levels[] __ro_after_init = {

Do you actually need this sort of renaming? Given that it is static,
this looks like some slightly abusive repainting which isn't warranted
here.

I also didn't understand the commit message: you're not tracking any
mask here, but a page table level. You are also not using it for
anything yet, see below.


>  	{ /* pgd */
>  		.name	= "PGD",
>  		.bits	= pte_bits,
> @@ -192,6 +192,7 @@ void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
>  	       u64 val)
>  {
>  	struct ptdump_pg_state *st = container_of(pt_st, struct ptdump_pg_state, ptdump);
> +	struct ptdump_pg_level *pg_level = st->pg_level;

This is what I mean. What is this pg_level used for?

>  	static const char units[] = "KMGTPE";
>  	u64 prot = 0;
>  
> @@ -262,6 +263,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
>  		.seq = s,
>  		.marker = info->markers,
>  		.mm = info->mm,
> +		.pg_level = &kernel_pg_levels[0],
>  		.level = -1,
>  		.ptdump = {
>  			.note_page = note_page,
> @@ -279,10 +281,10 @@ static void __init ptdump_initialize(void)
>  {
>  	unsigned i, j;
>  
> -	for (i = 0; i < ARRAY_SIZE(pg_level); i++)
> -		if (pg_level[i].bits)
> -			for (j = 0; j < pg_level[i].num; j++)
> -				pg_level[i].mask |= pg_level[i].bits[j].mask;
> +	for (i = 0; i < ARRAY_SIZE(kernel_pg_levels); i++)
> +		if (kernel_pg_levels[i].bits)
> +			for (j = 0; j < kernel_pg_levels[i].num; j++)
> +				kernel_pg_levels[i].mask |= kernel_pg_levels[i].bits[j].mask;
>  }
>  
>  static struct ptdump_info kernel_ptdump_info __ro_after_init = {
> @@ -297,6 +299,7 @@ bool ptdump_check_wx(void)
>  			{ 0, NULL},
>  			{ -1, NULL},
>  		},
> +		.pg_level = &kernel_pg_levels[0],
>  		.level = -1,
>  		.check_wx = true,
>  		.ptdump = {

Thanks,

	M.

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