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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Jia He <justin.he@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	linux-mm@kvack.org
Subject: Re: bug: data corruption introduced by commit 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is cleared")
Date: Thu, 13 Feb 2020 15:14:16 +0300	[thread overview]
Message-ID: <20200213121416.57ddim2ygktctjrl@box> (raw)
In-Reply-To: <x491rqz3myc.fsf@segfault.boston.devel.redhat.com>

On Wed, Feb 12, 2020 at 09:22:03AM -0500, Jeff Moyer wrote:
> "Kirill A. Shutemov" <kirill@shutemov.name> writes:
> 
> > On Tue, Feb 11, 2020 at 11:27:36AM -0500, Jeff Moyer wrote:
> >> > The real solution would be to retry __copy_from_user_inatomic() under ptl
> >> > if the first attempt fails. I expect it to be ugly.
> >> 
> >> So long as it's correct.  :)
> >
> > The first attempt on the real solution is below.
> >
> > Yeah, this is ugly. Any suggestion on clearing up this mess is welcome.
> >
> > Jeff, could you give it a try?
> 
> Yes, that patch appears to fix the problem.  I wonder if we could remove
> the clear_page completely, though.  I'd rather see the program segfault
> than operate on bad data.  What do you think?

It is long standing policy: see 6aab341e0a28 ("mm: re-architect the
VM_UNPAGED logic") from 2005. Some obscure case may break if change it.

I think it is fine to live with the WARN for a while and change it to
SIGBUS once we can be relatively sure that it is okay.

-- 
 Kirill A. Shutemov


  reply	other threads:[~2020-02-13 12:14 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10 22:51 bug: data corruption introduced by commit 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is cleared") Jeff Moyer
2020-02-11  4:17 ` Justin He
2020-02-11  4:29   ` Justin He
2020-02-11 16:44     ` Jeff Moyer
2020-02-11 17:33       ` Kirill A. Shutemov
2020-02-11 17:55         ` Jeff Moyer
2020-02-11 21:44           ` Kirill A. Shutemov
2020-02-11 22:01             ` Jeff Moyer
2020-02-11 22:15               ` Kirill A. Shutemov
2020-02-11 14:51 ` Kirill A. Shutemov
2020-02-11 16:27   ` Jeff Moyer
2020-02-11 22:40     ` Kirill A. Shutemov
2020-02-12 14:22       ` Jeff Moyer
2020-02-13 12:14         ` Kirill A. Shutemov [this message]
2020-02-14 21:07           ` Jeff Moyer

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