linux-kernel - Re: [PATCH] arm64: ptdump: Allow dumping user page tables

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Message-ID: <20211019123307.GA20031@axis.com>
Date:   Tue, 19 Oct 2021 14:33:08 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Will Deacon <will@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        kernel <kernel@...s.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: ptdump: Allow dumping user page tables

On Tue, Oct 19, 2021 at 02:09:32PM +0200, Will Deacon wrote:
> On Fri, Oct 01, 2021 at 04:56:03PM +0200, Vincent Whitchurch wrote:
> > Add a user_page_tables debugfs file (similar to kernel_page_tables) to
> > dump out the userspace page tables for the current process.  This
> > provides details which are not available via pagemap (such as the memory
> > type) and is useful when, for example, debugging ->mmap()
> > implementations.
> > 
> > Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> > ---
> >  arch/arm64/mm/ptdump.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> How does this serialise with things like task exit?

A task can only read its own page tables using this file, and the mm
lock is held during the walk in ptdump_walk_pgd().  Isn't that
sufficient?