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

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Message-ID: <ZsSkh2iw8s5Oa5xb@google.com>
Date: Tue, 20 Aug 2024 14:13:27 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Marc Zyngier <maz@...nel.org>
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 Tue, Aug 20, 2024 at 02:49:04PM +0100, Marc Zyngier wrote:
> 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 = {

Hi Marc,

 
> 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 applied Will's suggestion from
https://lore.kernel.org/all/20240705111229.GB9231@willie-the-truck/
>
> 
> 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.

and I missed updating the commit message.

> 
> 
> >  	{ /* 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?

I make use of it to extract the name based on the level. The suggestion
that Will made allowed me to keep the code with less changes.

Thanks,
Seb

> 
> >  	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.