linux-kernel - Re: [PATCH v12 0/4] fix double page fault in cow_user

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Date:   Wed, 16 Oct 2019 15:32:52 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Jia He <justin.he@....com>, Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Marc Zyngier <maz@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Suzuki Poulose <Suzuki.Poulose@....com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>, hejianet@...il.com,
        Kaly Xin <Kaly.Xin@....com>, nd@....com
Subject: Re: [PATCH v12 0/4] fix double page fault in cow_user_page for pfn
 mapping

On Tue, Oct 15, 2019 at 01:18:34AM +0100, Will Deacon wrote:
> On Fri, Oct 11, 2019 at 10:09:35PM +0800, Jia He wrote:
> > When we tested pmdk unit test vmmalloc_fork TEST1 in arm64 guest, there
> > will be a double page fault in __copy_from_user_inatomic of cow_user_page.
> > 
> > As told by Catalin: "On arm64 without hardware Access Flag, copying from
> > user will fail because the pte is old and cannot be marked young. So we
> > always end up with zeroed page after fork() + CoW for pfn mappings. we
> > don't always have a hardware-managed access flag on arm64."
> > 
> > -Changes
> > v12:
> >     refine PATCH 01, remove the !! since C languages can convert unsigned
> >     to bool (Catalin)
> 
> Thanks. I think it's a bit late to take something like this for 5.4 now,
> especially as the current behaviour has always been there. Hopefully
> somebody can queue it for 5.5 instead.

I can queue this through the arm64 tree for 5.5 if I get an ack on the
x86 patch (3/4) or I don't hear any complaints.

-- 
Catalin