linux-kernel - Re: [PATCH 0/4] mm: permit guard regions for file-backed/shmem mappings

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Message-ID: <CAC_TJve7NVqT5atUgdRkFN+U65RY8HYcfXx_CD8rxjra342-Yg@mail.gmail.com>
Date: Fri, 21 Feb 2025 09:24:59 -0800
From: Kalesh Singh <kaleshsingh@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>, David Hildenbrand <david@...hat.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, 
	Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>, 
	"Paul E . McKenney" <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Shuah Khan <shuah@...nel.org>, 
	linux-kselftest@...r.kernel.org, linux-api@...r.kernel.org, 
	John Hubbard <jhubbard@...dia.com>, Juan Yescas <jyescas@...gle.com>
Subject: Re: [PATCH 0/4] mm: permit guard regions for file-backed/shmem mappings

On Fri, Feb 21, 2025 at 3:04 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> On Thu, Feb 20, 2025 at 10:08:36AM -0800, Kalesh Singh wrote:
> > On Thu, Feb 20, 2025 at 8:22 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > >
> > > On Thu, Feb 20, 2025 at 5:18 AM Lorenzo Stoakes
> > > <lorenzo.stoakes@...cle.com> wrote:
> > > >
> > > > On Thu, Feb 20, 2025 at 01:44:20PM +0100, David Hildenbrand wrote:
> > > > > On 20.02.25 11:15, Lorenzo Stoakes wrote:
> > > > > > On Thu, Feb 20, 2025 at 11:03:02AM +0100, David Hildenbrand wrote:
> > > > > > > > > Your conclusion is 'did not participate with upstream'; I don't agree with
> > > > > > > > > that. But maybe you and Kalesh have a history on that that let's you react
> > > > > > > > > on his questions IMHO more emotionally than it should have been.
> > > > > > > >
> > > > > > > > This is wholly unfair, I have been very reasonable in response to this
> > > > > > > > thread. I have offered to find solutions, I have tried to understand the
> > > > > > > > problem in spite of having gone to great lengths to try to discuss the
> > > > > > > > limitations of the proposed approach in every venue I possibly could.
> > > > > > > >
> > > > > > > > I go out of my way to deal professionally and objectively with what is
> > > > > > > > presented. Nothing here is emotional. So I'd ask that you please abstain
> > > > > > > > from making commentary like this which has no basis.
> > > > > > >
> > > > > > > I appreciate everything you write below. But this request is just
> > > > > > > impossible. I will keep raising my opinion and misunderstandings will
> > > > > > > happen.
> > > > > >
> > > > > > Well I wouldn't ask you not to express your opinion David, you know I respect
> > > > > > and like you, and by all means push back hard or call out what you think is bad
> > > > > > behaviour :)
> > > > > >
> > > > > > I just meant to say, in my view, that there was no basis, but I appreciate
> > > > > > miscommunications happen.
> > > > > > > So apologies if I came off as being difficult or rude, it actually
> > > > > wasn't
> > > > > > intended. And to re-emphasise - I have zero personal issue with anybody in this
> > > > > > thread whatsoever!
> > > > >
> > > > > It sounded to me like you were trying to defend your work (again, IMHO too
> > > > > emotionally, and I might have completely misinterpreted that) and slowly
> > > > > switching to "friendly fire" (towards me). Apologies from my side if I
> > > > > completely misunderstood/misinterpreted that.
> > > >
> > > > Right this was not at all my intent, sorry if it seemed that way. I may well
> > > > have communicated terribly, so apologies on my side too.
> >
> > Hi everyone,
> >
> > Thank you for all the discussion.
> >
> > I don't find any personal issues with the communication in this
> > thread, but I appreciate David being the object voice of reason.
> >
> > I understand it can be frustrating since you have made many efforts to
> > communicate these tradeoffs. Unfortunately these issues were not known
> > for the file-backed ELF guard regions for my particular use case.
> >
> > >
> > > Sorry for being late to the party. Was sick for a couple of days.
> > > Lorenzo is right, there was a breakdown in communication at Google and
> > > he has all the rights to be upset. The issue with obfuscators should
> > > have been communicated once it was discovered. I was in regular
> > > discussions with Lorenzo but wasn't directly involved with this
> > > particular project and wasn't aware or did not realize that the
> > > obfuscator issue renders guards unusable for this usecase. My
> > > apologies, I should have asked more questions about it. I suspect
> > > Lorenzo would have implemented this anyway...
> > >
> >
> > Suren's use case is different from mine and this design fits perfectly
> > for anon guard regions from the allocator. :)
> >
> > So I think in conclusion, these aren't VMAs and shouldn't be treated
> > as such; we will advertise them from pagemap for those who need to
> > know.
> >
>
> Thanks Kalesh, glad there were no issues here and we have found
> constructive common ground! :)
>
> It turns out implementing the pagemap side of things is _really_
> straightforward, so I'll be sending a series for that shortly. Hopefully
> this provides some basis for whichever use cases need this information, as
> it is the best and least invasive place for this information at this stage.

Hi Lorenzo,

Reviewed your patches, agreed that is the cleanest way to advertise
this information.

Thanks,
Kalesh

>
> Cheers, Lorenzo
>
> > -- Kalesh