From: "Justin He (Arm Technology China)" <Justin.He@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>,
Mark Rutland <Mark.Rutland@arm.com>,
James Morse <James.Morse@arm.com>, Marc Zyngier <maz@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Punit Agrawal <punitagrawal@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
"hejianet@gmail.com" <hejianet@gmail.com>,
"Kaly Xin (Arm Technology China)" <Kaly.Xin@arm.com>,
nd <nd@arm.com>
Subject: RE: [PATCH v10 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
Date: Tue, 8 Oct 2019 02:19:05 +0000 [thread overview]
Message-ID: <DB7PR08MB3082563BD18482E5D541F019F79A0@DB7PR08MB3082.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20191001125413.mhxa6qszwnuhglky@willie-the-truck>
Hi Will
> -----Original Message-----
> From: Will Deacon <will@kernel.org>
> Sent: 2019年10月1日 20:54
> To: Justin He (Arm Technology China) <Justin.He@arm.com>
> Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Mark Rutland
> <Mark.Rutland@arm.com>; James Morse <James.Morse@arm.com>; Marc
> Zyngier <maz@kernel.org>; Matthew Wilcox <willy@infradead.org>; Kirill A.
> Shutemov <kirill.shutemov@linux.intel.com>; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; Punit Agrawal <punitagrawal@gmail.com>; Thomas
> Gleixner <tglx@linutronix.de>; Andrew Morton <akpm@linux-
> foundation.org>; hejianet@gmail.com; Kaly Xin (Arm Technology China)
> <Kaly.Xin@arm.com>
> Subject: Re: [PATCH v10 3/3] mm: fix double page fault on arm64 if PTE_AF
> is cleared
>
> On Mon, Sep 30, 2019 at 09:57:40AM +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
> >
> > Signed-off-by: Jia He <justin.he@arm.com>
> > Reported-by: Yibo Cai <Yibo.Cai@arm.com>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> > mm/memory.c | 99
> +++++++++++++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 84 insertions(+), 15 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index b1ca51a079f2..1f56b0118ef5 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -118,6 +118,13 @@ int randomize_va_space __read_mostly =
> > 2;
> > #endif
> >
> > +#ifndef arch_faults_on_old_pte
> > +static inline bool arch_faults_on_old_pte(void)
> > +{
> > + return false;
> > +}
> > +#endif
>
> Kirill has acked this, so I'm happy to take the patch as-is, however isn't
> it the case that /most/ architectures will want to return true for
> arch_faults_on_old_pte()? In which case, wouldn't it make more sense for
> that to be the default, and have x86 and arm64 provide an override? For
> example, aren't most architectures still going to hit the double fault
> scenario even with your patch applied?
No, after applying my patch series, only those architectures which don't provide
setting access flag by hardware AND don't implement their arch_faults_on_old_pte
will hit the double page fault.
The meaning of true for arch_faults_on_old_pte() is "this arch doesn't have the hardware
setting access flag way, it might cause page fault on an old pte"
I don't want to change other architectures' default behavior here. So by default,
arch_faults_on_old_pte() is false.
Btw, currently I only observed this double pagefault on arm64's guest (host is ThunderX2).
On X86 guest (host is Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz ), there is no such double
pagefault. It has the similar setting access flag way by hardware.
--
Cheers,
Justin (Jia He)
next prev parent reply other threads:[~2019-10-08 2:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-30 1:57 [PATCH v10 0/3] fix double page fault on arm64 Jia He
2019-09-30 1:57 ` [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-10-01 12:54 ` Will Deacon
2019-10-01 13:18 ` Marc Zyngier
2019-10-08 1:12 ` Justin He (Arm Technology China)
2019-10-08 15:32 ` Suzuki K Poulose
2019-10-09 6:29 ` Jia He
2019-09-30 1:57 ` [PATCH v10 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-10-01 12:50 ` Will Deacon
2019-10-01 13:32 ` Marc Zyngier
2019-10-08 1:55 ` Justin He (Arm Technology China)
2019-10-08 2:30 ` Justin He (Arm Technology China)
2019-10-08 7:46 ` Marc Zyngier
2019-09-30 1:57 ` [PATCH v10 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-10-01 12:54 ` Will Deacon
2019-10-08 2:19 ` Justin He (Arm Technology China) [this message]
2019-10-08 12:39 ` Will Deacon
2019-10-08 12:58 ` Justin He (Arm Technology China)
2019-10-08 14:32 ` Kirill A. Shutemov
2019-10-16 23:21 ` Palmer Dabbelt
2019-10-16 23:46 ` Will Deacon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=DB7PR08MB3082563BD18482E5D541F019F79A0@DB7PR08MB3082.eurprd08.prod.outlook.com \
--to=justin.he@arm.com \
--cc=Catalin.Marinas@arm.com \
--cc=James.Morse@arm.com \
--cc=Kaly.Xin@arm.com \
--cc=Mark.Rutland@arm.com \
--cc=akpm@linux-foundation.org \
--cc=hejianet@gmail.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=maz@kernel.org \
--cc=nd@arm.com \
--cc=punitagrawal@gmail.com \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).