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

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Message-ID: <ZsSqlIVsSylHaGaW@google.com>
Date: Tue, 20 Aug 2024 14:39:16 +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 03:25:13PM +0100, Marc Zyngier wrote:
> 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.

Yes, let me re-write the commit message in the next version,

Thanks,
Seb

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