From: Andy Lutomirski <luto@kernel.org>
To: Mike Rapoport <rppt@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
James Bottomley <jejb@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Linux API <linux-api@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, X86 ML <x86@kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings
Date: Tue, 29 Oct 2019 10:00:55 -0700 [thread overview]
Message-ID: <CALCETrUuuc4DS0cdMBtS550Wkp0x9ND3M3SgtaMgyRROnDR5Kg@mail.gmail.com> (raw)
In-Reply-To: <20191029093254.GE18773@rapoport-lnx>
On Tue, Oct 29, 2019 at 2:33 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Mon, Oct 28, 2019 at 02:44:23PM -0600, Andy Lutomirski wrote:
> >
> > > On Oct 27, 2019, at 4:17 AM, Mike Rapoport <rppt@kernel.org> wrote:
> > >
> > > From: Mike Rapoport <rppt@linux.ibm.com>
> > >
> > > Hi,
> > >
> > > The patch below aims to allow applications to create mappins that have
> > > pages visible only to the owning process. Such mappings could be used to
> > > store secrets so that these secrets are not visible neither to other
> > > processes nor to the kernel.
> > >
> > > I've only tested the basic functionality, the changes should be verified
> > > against THP/migration/compaction. Yet, I'd appreciate early feedback.
> >
> > I’ve contemplated the concept a fair amount, and I think you should
> > consider a change to the API. In particular, rather than having it be a
> > MAP_ flag, make it a chardev. You can, at least at first, allow only
> > MAP_SHARED, and admins can decide who gets to use it. It might also play
> > better with the VM overall, and you won’t need a VM_ flag for it — you
> > can just wire up .fault to do the right thing.
>
> I think mmap()/mprotect()/madvise() are the natural APIs for such
> interface.
Then you have a whole bunch of questions to answer. For example:
What happens if you mprotect() or similar when the mapping is already
in use in a way that's incompatible with MAP_EXCLUSIVE?
Is it actually reasonable to malloc() some memory and then make it exclusive?
Are you permitted to map a file MAP_EXCLUSIVE? What does it mean?
What does MAP_PRIVATE | MAP_EXCLUSIVE do?
How does one pass exclusive memory via SCM_RIGHTS? (If it's a
memfd-like or chardev interface, it's trivial. mmap(), not so much.)
And finally, there's my personal giant pet peeve: a major use of this
will be for virtualization. I suspect that a lot of people would like
the majority of KVM guest memory to be unmapped from the host
pagetables. But people might also like for guest memory to be
unmapped in *QEMU's* pagetables, and mmap() is a basically worthless
interface for this. Getting fd-backed memory into a guest will take
some possibly major work in the kernel, but getting vma-backed memory
into a guest without mapping it in the host user address space seems
much, much worse.
> Switching to a chardev doesn't solve the major problem of direct
> map fragmentation and defeats the ability to use exclusive memory mappings
> with the existing allocators, while mprotect() and madvise() do not.
>
Will people really want to do malloc() and then remap it exclusive?
This sounds dubiously useful at best.
next prev parent reply other threads:[~2019-10-29 17:01 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-27 10:17 [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Mike Rapoport
2019-10-27 10:17 ` Mike Rapoport
2019-10-28 12:31 ` Kirill A. Shutemov
2019-10-28 13:00 ` Mike Rapoport
2019-10-28 13:16 ` Kirill A. Shutemov
2019-10-28 13:55 ` Peter Zijlstra
2019-10-28 19:59 ` Edgecombe, Rick P
2019-10-28 21:00 ` Peter Zijlstra
2019-10-29 17:27 ` Edgecombe, Rick P
2019-10-30 10:04 ` Peter Zijlstra
2019-10-30 15:35 ` Alexei Starovoitov
2019-10-30 18:39 ` Peter Zijlstra
2019-10-30 18:52 ` Alexei Starovoitov
2019-10-30 17:48 ` Edgecombe, Rick P
2019-10-30 17:58 ` Dave Hansen
2019-10-30 18:01 ` Dave Hansen
2019-10-29 5:43 ` Dan Williams
2019-10-29 6:43 ` Kirill A. Shutemov
2019-10-29 8:56 ` Peter Zijlstra
2019-10-29 11:00 ` Kirill A. Shutemov
2019-10-29 12:39 ` AMD TLB errata, (Was: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings) Peter Zijlstra
2019-11-15 14:12 ` Tom Lendacky
2019-11-15 14:31 ` Peter Zijlstra
2019-10-29 19:43 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Dan Williams
2019-10-29 20:07 ` Dave Hansen
2019-10-29 7:08 ` Christopher Lameter
2019-10-29 8:55 ` Mike Rapoport
2019-10-29 10:12 ` Christopher Lameter
2019-10-30 7:11 ` Mike Rapoport
2019-10-30 12:09 ` Christopher Lameter
2019-10-28 14:55 ` David Hildenbrand
2019-10-28 17:12 ` Dave Hansen
2019-10-28 17:32 ` Sean Christopherson
2019-10-28 18:08 ` Matthew Wilcox
2019-10-29 9:28 ` Mike Rapoport
2019-10-29 9:19 ` Mike Rapoport
2019-10-28 18:02 ` Andy Lutomirski
2019-10-29 11:02 ` David Hildenbrand
2019-10-30 8:15 ` Mike Rapoport
2019-10-30 8:19 ` David Hildenbrand
2019-10-31 19:16 ` Mike Rapoport
2019-10-31 21:52 ` Dan Williams
2019-10-27 10:30 ` Florian Weimer
2019-10-27 11:00 ` Mike Rapoport
2019-10-28 20:23 ` Florian Weimer
2019-10-29 9:01 ` Mike Rapoport
2019-10-28 20:44 ` Andy Lutomirski
2019-10-29 9:32 ` Mike Rapoport
2019-10-29 17:00 ` Andy Lutomirski [this message]
2019-10-30 8:40 ` Mike Rapoport
2019-10-30 21:28 ` Andy Lutomirski
2019-10-31 7:21 ` Mike Rapoport
2019-12-05 15:34 ` Mike Rapoport
2019-12-08 14:10 ` [PATCH] mm: extend memfd with ability to create secret memory kbuild test robot
2019-10-29 11:25 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Reshetova, Elena
2019-10-29 15:13 ` Tycho Andersen
2019-10-29 17:03 ` Andy Lutomirski
2019-10-29 17:37 ` Alan Cox
2019-10-29 17:43 ` James Bottomley
2019-10-29 18:10 ` Andy Lutomirski
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