linux-kernel - RE: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE

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Date:   Fri, 20 Sep 2019 14:24:04 +0000
From:   "Justin He (Arm Technology China)" <Justin.He@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>, nd <nd@....com>,
        "hejianet@...il.com" <hejianet@...il.com>
Subject: RE: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is
 cleared

Thanks for your patent review 😊

--
Cheers,
Justin (Jia He)



> -----Original Message-----
> From: Kirill A. Shutemov <kirill@...temov.name>
> Sent: 2019年9月20日 22:21
> To: Justin He (Arm Technology China) <Justin.He@....com>
> Cc: Catalin Marinas <Catalin.Marinas@....com>; Will Deacon
> <will@...nel.org>; 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>; Punit Agrawal <punitagrawal@...il.com>;
> Anshuman Khandual <Anshuman.Khandual@....com>; Alex Van Brunt
> <avanbrunt@...dia.com>; Robin Murphy <Robin.Murphy@....com>;
> Thomas Gleixner <tglx@...utronix.de>; Andrew Morton <akpm@...ux-
> foundation.org>; Jérôme Glisse <jglisse@...hat.com>; Ralph Campbell
> <rcampbell@...dia.com>; hejianet@...il.com; Kaly Xin (Arm Technology
> China) <Kaly.Xin@....com>; nd <nd@....com>
> Subject: Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is
> cleared
> 
> On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote:
> > When we tested pmdk unit test [1] vmmalloc_fork TEST1 in arm64 guest,
> there
> > will be a double page fault in __copy_from_user_inatomic of
> cow_user_page.
> >
> > Below call trace is from arm64 do_page_fault for debugging purpose
> > [  110.016195] Call trace:
> > [  110.016826]  do_page_fault+0x5a4/0x690
> > [  110.017812]  do_mem_abort+0x50/0xb0
> > [  110.018726]  el1_da+0x20/0xc4
> > [  110.019492]  __arch_copy_from_user+0x180/0x280
> > [  110.020646]  do_wp_page+0xb0/0x860
> > [  110.021517]  __handle_mm_fault+0x994/0x1338
> > [  110.022606]  handle_mm_fault+0xe8/0x180
> > [  110.023584]  do_page_fault+0x240/0x690
> > [  110.024535]  do_mem_abort+0x50/0xb0
> > [  110.025423]  el0_da+0x20/0x24
> >
> > The pte info before __copy_from_user_inatomic is (PTE_AF is cleared):
> > [ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003,
> pmd=000000023d4b3003, pte=360000298607bd3
> >
> > 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."
> >
> > This patch fix it by calling pte_mkyoung. Also, the parameter is
> > changed because vmf should be passed to cow_user_page()
> >
> > Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error
> > in case there can be some obscure use-case.(by Kirill)
> >
> > [1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
> >
> > Reported-by: Yibo Cai <Yibo.Cai@....com>
> > Signed-off-by: Jia He <justin.he@....com>
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> --
>  Kirill A. Shutemov