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

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Message-ID: <86o75nxody.wl-maz@kernel.org>
Date: Tue, 20 Aug 2024 15:25:13 +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 Tue, 20 Aug 2024 15:13:27 +0100,
Sebastian Ene <sebastianene@...gle.com> wrote:
> 
> 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.

Err, I see that now. It'd be good if you described what actually
happens, because it is almost impossible to understand it from reading
the patch.

Thanks,

	M.

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