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From: Dmitry Safonov <0x7f454c46@gmail.com>
Date: Tue, 2 Jan 2018 16:44:22 +0000
Message-ID: <CAJwJo6ZujJah9rTnhogGBR-7B9t7vuXi7vBTn2N=N4bc-FL3hw@mail.gmail.com>
Subject: Re: [PATCH v2 02/17] mm: Exempt special mappings from mlock(),
 mprotect() and madvise()
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bpetkov@suse.de>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Denys Vlasenko <dvlasenk@redhat.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, David Laight <David.Laight@aculab.com>, Eduardo Valentin <eduval@amazon.com>, "Liguori, Anthony" <aliguori@amazon.com>, Will Deacon <will.deacon@arm.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>, crml <criu@openvz.org>

Hi, sorry for the late reply,

2017-12-14 17:36 GMT+00:00 Peter Zijlstra <peterz@infradead.org>:
> On Thu, Dec 14, 2017 at 08:19:36AM -0800, Andy Lutomirski wrote:
>> On Thu, Dec 14, 2017 at 3:27 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > It makes no sense to ever prod at special mappings with any of these
>> > syscalls.
>> >
>> > XXX should we include munmap() ?
>>
>> This is an ABI break for the vdso.  Maybe that's okay, but mremap() on
>> the vdso is certainly used, and I can imagine debuggers using
>> mprotect().
>
> *groan*, ok so mremap() will actually still work after this, but yes,
> mprotect() will not. I hadn't figured people would muck with the VDSO
> like that.

mremap() is needed for CRIU, at least.

Please, don't restrict munmap(), as ARCH_MAP_VDSO_* allows to map vdso
iff it's not already mapped.
We don't need +w vdso mapping, but I guess that may break gdb breakpoints
on vdso.

Also, AFAICS, vma_is_special_mapping() has two parameters in linux-next,
and your patches set doesn't change that.

Thanks,
             Dmitry

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