From: Chao Peng <chao.p.peng@linux.intel.com>
To: "Gupta, Pankaj" <pankaj.gupta@amd.com>
Cc: David Hildenbrand <david@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
qemu-devel@nongnu.org, linux-kselftest@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
Hugh Dickins <hughd@google.com>, Jeff Layton <jlayton@kernel.org>,
"J . Bruce Fields" <bfields@fieldses.org>,
Andrew Morton <akpm@linux-foundation.org>,
Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
Steven Price <steven.price@arm.com>,
"Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
Vlastimil Babka <vbabka@suse.cz>,
Vishal Annapurve <vannapurve@google.com>,
Yu Zhang <yu.c.zhang@linux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
ak@linux.intel.com, aarcange@redhat.com, ddutile@redhat.com,
dhildenb@redhat.com, Quentin Perret <qperret@google.com>,
Michael Roth <michael.roth@amd.com>,
mhocko@suse.com, Muchun Song <songmuchun@bytedance.com>
Subject: Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd
Date: Mon, 25 Jul 2022 21:54:16 +0800 [thread overview]
Message-ID: <20220725135416.GD304216@chaop.bj.intel.com> (raw)
In-Reply-To: <c59fca89-cd0c-1724-210e-d9b01b375103@amd.com>
On Thu, Jul 21, 2022 at 12:27:03PM +0200, Gupta, Pankaj wrote:
>
> > > Normally, a write to unallocated space of a file or the hole of a sparse
> > > file automatically causes space allocation, for memfd, this equals to
> > > memory allocation. This new seal prevents such automatically allocating,
> > > either this is from a direct write() or a write on the previously
> > > mmap-ed area. The seal does not prevent fallocate() so an explicit
> > > fallocate() can still cause allocating and can be used to reserve
> > > memory.
> > >
> > > This is used to prevent unintentional allocation from userspace on a
> > > stray or careless write and any intentional allocation should use an
> > > explicit fallocate(). One of the main usecases is to avoid memory double
> > > allocation for confidential computing usage where we use two memfds to
> > > back guest memory and at a single point only one memfd is alive and we
> > > want to prevent memory allocation for the other memfd which may have
> > > been mmap-ed previously. More discussion can be found at:
> > >
> > > https://lkml.org/lkml/2022/6/14/1255
> > >
> > > Suggested-by: Sean Christopherson <seanjc@google.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > > include/uapi/linux/fcntl.h | 1 +
> > > mm/memfd.c | 3 ++-
> > > mm/shmem.c | 16 ++++++++++++++--
> > > 3 files changed, 17 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> > > index 2f86b2ad6d7e..98bdabc8e309 100644
> > > --- a/include/uapi/linux/fcntl.h
> > > +++ b/include/uapi/linux/fcntl.h
> > > @@ -43,6 +43,7 @@
> > > #define F_SEAL_GROW 0x0004 /* prevent file from growing */
> > > #define F_SEAL_WRITE 0x0008 /* prevent writes */
> > > #define F_SEAL_FUTURE_WRITE 0x0010 /* prevent future writes while mapped */
> > > +#define F_SEAL_AUTO_ALLOCATE 0x0020 /* prevent allocation for writes */
> >
> > Why only "on writes" and not "on reads". IIRC, shmem doesn't support the
> > shared zeropage, so you'll simply allocate a new page via read() or on
> > read faults.
> >
> >
> > Also, I *think* you can place pages via userfaultfd into shmem. Not sure
> > if that would count "auto alloc", but it would certainly bypass fallocate().
>
> I was also thinking this at the same time, but for different reason:
>
> "Want to populate private preboot memory with firmware payload", so was
> thinking userfaulftd could be an option as direct writes are restricted?
If that can be a side effect, I definitely glad to see it, though I'm
still not clear how userfaultfd can be particularly helpful for that.
Chao
>
> Thanks,
> Pankaj
>
>
>
>
next prev parent reply other threads:[~2022-07-25 13:59 UTC|newest]
Thread overview: 172+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-06 8:20 [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Chao Peng
2022-07-06 8:20 ` [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd Chao Peng
2022-07-21 9:44 ` David Hildenbrand
2022-07-21 9:50 ` David Hildenbrand
2022-07-21 15:05 ` Sean Christopherson
2022-07-25 13:46 ` Chao Peng
2022-07-21 10:27 ` Gupta, Pankaj
2022-07-25 13:54 ` Chao Peng [this message]
2022-07-25 14:49 ` Gupta, Pankaj
2022-07-25 13:42 ` Chao Peng
2022-08-05 17:55 ` Paolo Bonzini
2022-08-05 18:06 ` David Hildenbrand
2022-08-10 9:40 ` Chao Peng
2022-08-10 9:38 ` Chao Peng
2022-08-17 23:41 ` Kirill A. Shutemov
2022-08-18 9:09 ` Paolo Bonzini
2022-08-23 7:36 ` David Hildenbrand
2022-08-24 10:20 ` Chao Peng
2022-08-26 15:19 ` Fuad Tabba
2022-08-29 15:18 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 02/14] selftests/memfd: Add tests for F_SEAL_AUTO_ALLOCATE Chao Peng
2022-08-05 13:11 ` David Hildenbrand
2022-07-06 8:20 ` [PATCH v7 03/14] mm: Introduce memfile_notifier Chao Peng
2022-08-05 13:22 ` David Hildenbrand
2022-08-10 9:22 ` Chao Peng
2022-08-10 10:05 ` David Hildenbrand
2022-08-10 14:38 ` Sean Christopherson
2022-08-11 12:27 ` Quentin Perret
2022-08-11 13:39 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 04/14] mm/shmem: Support memfile_notifier Chao Peng
2022-07-12 18:02 ` Gupta, Pankaj
2022-07-13 7:44 ` Chao Peng
2022-07-13 10:01 ` Gupta, Pankaj
2022-07-13 23:49 ` Chao Peng
2022-07-14 4:15 ` Gupta, Pankaj
2022-08-05 13:26 ` David Hildenbrand
2022-08-10 9:25 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 05/14] mm/memfd: Introduce MFD_INACCESSIBLE flag Chao Peng
2022-08-05 13:28 ` David Hildenbrand
2022-08-10 9:37 ` Chao Peng
2022-08-10 9:55 ` David Hildenbrand
2022-08-11 13:17 ` Chao Peng
2022-09-07 16:18 ` Kirill A. Shutemov
2022-07-06 8:20 ` [PATCH v7 06/14] KVM: Rename KVM_PRIVATE_MEM_SLOTS to KVM_INTERNAL_MEM_SLOTS Chao Peng
2022-07-06 8:20 ` [PATCH v7 07/14] KVM: Use gfn instead of hva for mmu_notifier_retry Chao Peng
2022-07-15 11:36 ` Gupta, Pankaj
2022-07-18 13:29 ` Chao Peng
2022-07-18 15:26 ` Sean Christopherson
2022-07-19 14:02 ` Chao Peng
2022-08-04 7:10 ` Isaku Yamahata
2022-08-10 8:19 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 08/14] KVM: Rename mmu_notifier_* Chao Peng
2022-07-29 19:02 ` Sean Christopherson
2022-08-03 10:13 ` Chao Peng
2022-08-05 19:54 ` Paolo Bonzini
2022-08-10 8:09 ` Chao Peng
2023-05-23 7:19 ` Kautuk Consul
2023-05-23 14:19 ` Sean Christopherson
2023-05-24 6:12 ` Kautuk Consul
2023-05-24 20:16 ` Sean Christopherson
2023-05-24 20:33 ` Peter Zijlstra
2023-05-24 21:39 ` Sean Christopherson
2023-05-25 8:54 ` Peter Zijlstra
2023-05-25 3:52 ` Kautuk Consul
2023-05-24 20:28 ` Peter Zijlstra
2022-07-06 8:20 ` [PATCH v7 09/14] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-07-29 19:51 ` Sean Christopherson
2022-08-03 10:08 ` Chao Peng
2022-08-03 14:42 ` Sean Christopherson
2022-07-06 8:20 ` [PATCH v7 10/14] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-07-06 8:20 ` [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions Chao Peng
2022-07-19 8:00 ` Gupta, Pankaj
2022-07-19 14:08 ` Chao Peng
2022-07-19 14:23 ` Gupta, Pankaj
2022-07-20 15:07 ` Chao Peng
2022-07-20 15:31 ` Gupta, Pankaj
2022-07-20 16:21 ` Sean Christopherson
2022-07-20 17:41 ` Gupta, Pankaj
2022-07-21 7:34 ` Wei Wang
2022-07-21 9:29 ` Chao Peng
2022-07-21 17:58 ` Sean Christopherson
2022-07-25 13:04 ` Chao Peng
2022-07-29 19:54 ` Sean Christopherson
2022-08-02 0:49 ` Sean Christopherson
2022-08-02 16:38 ` Sean Christopherson
2022-08-03 9:48 ` Chao Peng
2022-08-03 15:51 ` Sean Christopherson
2022-08-04 7:58 ` Chao Peng
2022-07-20 16:44 ` Sean Christopherson
2022-07-21 9:37 ` Chao Peng
2022-08-19 19:37 ` Vishal Annapurve
2022-08-24 10:37 ` Chao Peng
2022-08-26 15:19 ` Fuad Tabba
2022-08-29 15:21 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 12/14] KVM: Handle page fault for private memory Chao Peng
2022-07-29 20:58 ` Sean Christopherson
2022-08-03 9:52 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 13/14] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-07-19 9:55 ` Gupta, Pankaj
2022-07-19 14:12 ` Chao Peng
2022-07-06 8:20 ` [PATCH v7 14/14] memfd_create.2: Describe MFD_INACCESSIBLE flag Chao Peng
2022-08-01 14:40 ` Dave Hansen
2022-08-03 9:53 ` Chao Peng
2022-07-13 3:58 ` [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Gupta, Pankaj
2022-07-13 7:57 ` Chao Peng
2022-07-13 10:35 ` Gupta, Pankaj
2022-07-13 23:59 ` Chao Peng
2022-07-14 4:39 ` Gupta, Pankaj
2022-07-14 5:06 ` Gupta, Pankaj
2022-07-14 4:29 ` Andy Lutomirski
2022-07-14 5:13 ` Gupta, Pankaj
2022-08-11 10:02 ` Nikunj A. Dadhania
2022-08-11 11:30 ` Gupta, Pankaj
2022-08-11 13:32 ` Chao Peng
2022-08-11 17:28 ` Nikunj A. Dadhania
2022-08-12 3:22 ` Nikunj A. Dadhania
2022-08-11 17:18 ` Nikunj A. Dadhania
2022-08-11 23:02 ` Gupta, Pankaj
2022-08-12 6:02 ` Gupta, Pankaj
2022-08-12 7:18 ` Gupta, Pankaj
2022-08-12 8:48 ` Nikunj A. Dadhania
2022-08-12 9:33 ` Gupta, Pankaj
2022-08-15 13:04 ` Chao Peng
2022-08-16 4:28 ` Nikunj A. Dadhania
2022-08-16 11:33 ` Gupta, Pankaj
2022-08-16 12:24 ` Kirill A . Shutemov
2022-08-16 13:03 ` Gupta, Pankaj
2022-08-16 15:38 ` Sean Christopherson
2022-08-17 15:27 ` Michael Roth
2022-08-23 1:25 ` Isaku Yamahata
2022-08-23 17:41 ` Gupta, Pankaj
2022-08-18 5:40 ` Hugh Dickins
2022-08-18 13:24 ` Kirill A . Shutemov
2022-08-19 0:20 ` Sean Christopherson
2022-08-19 3:38 ` Hugh Dickins
2022-08-19 22:53 ` Sean Christopherson
2022-08-23 7:55 ` David Hildenbrand
2022-08-23 16:05 ` Sean Christopherson
2022-08-24 9:41 ` Chao Peng
2022-09-09 4:55 ` Andy Lutomirski
2022-08-19 3:00 ` Hugh Dickins
2022-08-20 0:27 ` Kirill A. Shutemov
2022-08-21 5:15 ` Hugh Dickins
2022-08-31 14:24 ` Kirill A . Shutemov
2022-09-02 10:27 ` Chao Peng
2022-09-02 12:30 ` Kirill A . Shutemov
2022-09-08 1:10 ` Kirill A. Shutemov
2022-09-13 9:44 ` Sean Christopherson
2022-09-13 13:28 ` Kirill A. Shutemov
2022-09-13 14:53 ` Sean Christopherson
2022-09-13 16:00 ` Kirill A. Shutemov
2022-09-13 16:12 ` Sean Christopherson
2022-09-09 4:48 ` Andy Lutomirski
2022-09-09 14:32 ` Kirill A . Shutemov
2022-09-09 19:11 ` Andy Lutomirski
2022-09-09 23:02 ` Kirill A . Shutemov
2022-08-21 10:27 ` Matthew Wilcox
2022-08-24 10:27 ` Chao Peng
2022-09-09 4:44 ` Andy Lutomirski
[not found] ` <diqzlej60z57.fsf@ackerleytng-cloudtop.c.googlers.com>
[not found] ` <20221202061347.1070246-2-chao.p.peng@linux.intel.com>
2023-04-13 15:25 ` Christian Brauner
2023-04-13 22:28 ` Sean Christopherson
2023-04-14 22:38 ` Ackerley Tng
2023-04-14 23:26 ` Sean Christopherson
2023-04-15 0:06 ` Sean Christopherson
2023-04-19 8:29 ` Christian Brauner
2023-04-20 0:49 ` Sean Christopherson
2023-04-20 8:35 ` Christian Brauner
2022-08-26 15:19 ` Fuad Tabba
2022-08-29 15:17 ` Chao Peng
2022-08-31 9:12 ` Fuad Tabba
2022-09-02 10:19 ` Chao Peng
2022-09-09 15:35 ` Michael Roth
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