linux-kernel - Re: [PATCH v6 03/23] mm: Check against orig_pte for finish

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Message-ID: <Ybry+cBqY71/Y3OT@xz-m1.local>
Date:   Thu, 16 Dec 2021 16:04:09 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Hugh Dickins <hughd@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Jerome Glisse <jglisse@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v6 03/23] mm: Check against orig_pte for finish_fault()

On Thu, Dec 16, 2021 at 06:45:07PM +1100, Alistair Popple wrote:
> On Thursday, 16 December 2021 6:06:54 PM AEDT Peter Xu wrote:
> 
> [...]
> 
> > I wondered how it could have worked - I thought e.g. pte_alloc_one() will
> > always return a pgtable page will all zero-filled, whose allocation should
> > require __GFP_ZERO anyway.  But then I quickly noticed that pte_alloc_one() is
> > per-arch too..  That explains, because per-arch can re-initialize the default
> > pte values.
> 
> Yes, I have wondered the same things before as well. It's all a little bit of
> fun some of this stuff.
> 
> > I thought this patch can greatly simplify things but I overlooked the
> > pte_none() check you mentioned.  So it seems I have no good choice but add that
> > flag back.
> > 
> > There's another alternative is we do pte_clear() on vmf->orig_pte as the new
> > way to initialize it.  I believe it should work too for s390 and xtensa.
> > 
> > Any preference?
> 
> I prefer the later approach (initialising to pte_clear) as it seems cleaner,
> and pte_none(pte_clear()) is true for every architecture afaik.

Will do.

-- 
Peter Xu