Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 31 Jul 2023 20:40:24 +0100
From:   Lorenzo Stoakes <lstoakes@gmail.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Baoquan He <bhe@redhat.com>, Jiri Olsa <olsajiri@gmail.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Liu Shixin <liushixin2@huawei.com>,
        Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data
Message-ID: <b8b05bb6-3d23-4e90-beb0-a256dbc32ef2@lucifer.local>
References: <cover.1679566220.git.lstoakes@gmail.com>
 <fd39b0bfa7edc76d360def7d034baaee71d90158.1679566220.git.lstoakes@gmail.com>
 <ZHc2fm+9daF6cgCE@krava>
 <ZLqMtcPXAA8g/4JI@MiWiFi-R3L-srv>
 <86fd0ccb-f460-651f-8048-1026d905a2d6@redhat.com>
 <f10f06d4-9c82-41d3-a62a-09c62f254cfc@lucifer.local>
 <32b8c5e4-c8e3-0244-1b1a-ca33bd44f38a@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <32b8c5e4-c8e3-0244-1b1a-ca33bd44f38a@redhat.com>
Precedence: bulk

On Mon, Jul 31, 2023 at 09:24:50PM +0200, David Hildenbrand wrote:
> On 31.07.23 21:21, Lorenzo Stoakes wrote:
> > On Mon, Jul 24, 2023 at 08:23:55AM +0200, David Hildenbrand wrote:
> > > Hi,
> > >
> > > >
> > > > I met this too when I executed below command to trigger a kcore reading.
> > > > I wanted to do a simple testing during system running and got this.
> > > >
> > > >     makedumpfile --mem-usage /proc/kcore
> > > >
> > > > Later I tried your above objdump testing, it corrupted system too.
> > > >
> > >
> > > What do you mean with "corrupted system too" --  did it not only fail to
> > > dump the system, but also actually harmed the system?
> > >
> > > @Lorenzo do you plan on reproduce + fix, or should we consider reverting
> > > that change?
> > >
> > > --
> > > Cheers,
> > >
> > > David / dhildenb
> > >
> >
> > Apologies I mised this, I have been very busy lately not least with book :)
> >
> > Concerning, I will take a look as I get a chance. I think the whole series
> > would have to be reverted which would be... depressing... as other patches
> > in series eliminates the bounce buffer altogether.
> >
>
> I spotted
>
> https://lkml.kernel.org/r/069dd40aa71e634b414d07039d72467d051fb486.camel@gmx.de
>

Find that slightly confusing, they talk about just reveritng the patch but then
also add a kern_addr_valid()?

I'm also confused about people talking about just reverting the patch, as
4c91c07c93bb drops the bounce buffer altogether... presumably they mean
reverting both?

Clearly this is an arm64 thing (obviously), I have some arm64 hardware let me
see if I can repro...

Baoquan, Jiri - are you reverting more than just the one commit? And does doing
this go from not working -> working? Or from not working (worst case oops) ->
error?

> today, maybe that's related.
>
> --
> Cheers,
>
> David / dhildenb
>