linux-kernel - Re: [PATCH v2] mm: fix double page fault on arm64 if PTE

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Date:   Mon, 9 Sep 2019 14:27:12 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Jia He <justin.he@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Airlie <airlied@...hat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Souptick Joarder <jrdr.linux@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is
 cleared

On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> +		if (!pte_young(vmf->orig_pte)) {
> +			entry = pte_mkyoung(vmf->orig_pte);
> +			if (ptep_set_access_flags(vmf->vma, vmf->address,
> +				vmf->pte, entry, 0))
> +				update_mmu_cache(vmf->vma, vmf->address,
> +						vmf->pte);
> +		}
> +

Oh, btw, why call update_mmu_cache() here?  All you've done is changed
the 'accessed' bit.  What is any architecture supposed to do in response
to this?