linux-kernel - Re: [PATCH 5/5] ptdump: add state parameter for non-leaf callback

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Date: Tue, 16 Apr 2024 21:01:51 +0000
From: Maxwell Bland <mbland@...orola.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Catalin Marinas
	<catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Michael Ellerman
	<mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy
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        Aneesh Kumar K.V <aneesh.kumar@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
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        Albert Ou
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Subject: Re: [PATCH 5/5] ptdump: add state parameter for non-leaf callback

> On Tuesday, April 16, 2024 3:11 PM, Andrew Morton wrote:
> On Mon, 15 Apr 2024 14:51:32 -0500 Maxwell Bland <mbland@...orola.com>
> wrote:
>
> >  arch/arm64/mm/ptdump.c          |  6 ++++--
> >  arch/powerpc/mm/ptdump/ptdump.c |  2 ++
> >  arch/riscv/mm/ptdump.c          |  6 ++++--
> >  arch/s390/mm/dump_pagetables.c  |  6 ++++--
> >  arch/x86/mm/dump_pagetables.c   |  3 ++-
> >  include/linux/ptdump.h          |  1 +
> >  mm/ptdump.c                     | 13 +++++++++++++
> >  7 files changed, 30 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> > index 796231a4fd63..1a6f4a3513e5 100644
> > --- a/arch/arm64/mm/ptdump.c
> > +++ b/arch/arm64/mm/ptdump.c
> > @@ -299,7 +299,8 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info
> *info)
> >                     .range = (struct ptdump_range[]){
> >                             {info->base_addr, end},
> >                             {0, 0}
> > -                   }
> > +                   },
> > +                   .note_non_leaf = false
> >             }
>
> It would be acceptable to omit all of these and rely upon the runtime
> zeroing which the compiler will emit.

Ah, thank you for the pointer to C99 6.7.8.21. I had always figured since
structs are stack allocated they are potentially non-initialized!

> Documentation/arch/arm64/ptdump.rst might need updating.
>
> Please include sample output in the changelog so we can better
> understand the user's view of this change.

Thanks, I will do both in the next few days everything permitting! Right now
this patch results in no change until note_non_leaf = true is adopted for each
arch.

My plan: I will polish then include output of my personal fixes for arm64.
Specifically, printing expanded PMD flags and tab indenting the layout
according to each level.

Hopefully just adding arm64 support for now is OK, unless maybe we want to
default this to true on all arches? IMO default true would be sweet, but I
wasn't sure everyone would agree.

BRs,
Maxwell Bland