linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Chao Peng <chao.p.peng@linux.intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	qemu-devel@nongnu.org, Linux API <linux-api@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>,
	Yu Zhang <yu.c.zhang@linux.intel.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	jun.nakajima@intel.com, dave.hansen@intel.com,
	ak@linux.intel.com, david@redhat.com
Subject: Re: [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE
Date: Thu, 17 Feb 2022 21:06:31 +0800	[thread overview]
Message-ID: <20220217130631.GB32679@chaop.bj.intel.com> (raw)
In-Reply-To: <619547ad-de96-1be9-036b-a7b4e99b09a6@kernel.org>

On Fri, Feb 11, 2022 at 03:33:35PM -0800, Andy Lutomirski wrote:
> On 1/18/22 05:21, Chao Peng wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > 
> > Introduce a new seal F_SEAL_INACCESSIBLE indicating the content of
> > the file is inaccessible from userspace through ordinary MMU access
> > (e.g., read/write/mmap). However, the file content can be accessed
> > via a different mechanism (e.g. KVM MMU) indirectly.
> > 
> > It provides semantics required for KVM guest private memory support
> > that a file descriptor with this seal set is going to be used as the
> > source of guest memory in confidential computing environments such
> > as Intel TDX/AMD SEV but may not be accessible from host userspace.
> > 
> > At this time only shmem implements this seal.
> > 
> 
> I don't dislike this *that* much, but I do dislike this. F_SEAL_INACCESSIBLE
> essentially transmutes a memfd into a different type of object.  While this
> can apparently be done successfully and without races (as in this code),
> it's at least awkward.  I think that either creating a special inaccessible
> memfd should be a single operation that create the correct type of object or
> there should be a clear justification for why it's a two-step process.

Now one justification maybe from Stever's comment to patch-00: for ARM
usage it can be used with creating a normal memfd, (partially)populate
it with initial guest memory content (e.g. firmware), and then
F_SEAL_INACCESSIBLE it just before the first time lunch of the guest in
KVM (definitely the current code needs to be changed to support that).

Thanks,
Chao
> 
> (Imagine if the way to create an eventfd would be to call timerfd_create()
> and then do a special fcntl to turn it into an eventfd but only if it's not
> currently armed.  This would be weird.)


  reply	other threads:[~2022-02-17 13:07 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-18 13:21 [PATCH v4 00/12] KVM: mm: fd-based approach for supporting KVM guest private memory Chao Peng
2022-01-18 13:21 ` [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE Chao Peng
2022-02-07 12:24   ` Vlastimil Babka
2022-02-17 12:56     ` Chao Peng
2022-02-11 23:33   ` Andy Lutomirski
2022-02-17 13:06     ` Chao Peng [this message]
2022-02-17 19:09       ` Andy Lutomirski
2022-02-23 11:49         ` Chao Peng
2022-02-23 12:05           ` Steven Price
2022-03-04 19:24             ` Andy Lutomirski
2022-03-07 13:26               ` Chao Peng
2022-03-08 12:17                 ` Paolo Bonzini
2022-01-18 13:21 ` [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag Chao Peng
2022-01-21 15:50   ` Steven Price
2022-01-24 13:29     ` Chao Peng
2022-02-07 18:51   ` Vlastimil Babka
2022-02-08  8:49     ` David Hildenbrand
2022-02-08 18:22       ` Mike Rapoport
2022-01-18 13:21 ` [PATCH v4 03/12] mm: Introduce memfile_notifier Chao Peng
2022-03-07 15:42   ` Vlastimil Babka
2022-03-08  1:45     ` Chao Peng
2022-01-18 13:21 ` [PATCH v4 04/12] mm/shmem: Support memfile_notifier Chao Peng
2022-02-08 18:29   ` Mike Rapoport
2022-02-17 13:10     ` Chao Peng
2022-02-11 23:40   ` Andy Lutomirski
2022-02-17 13:23     ` Chao Peng
2022-01-18 13:21 ` [PATCH v4 05/12] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-01-18 13:21 ` [PATCH v4 06/12] KVM: Use kvm_userspace_memory_region_ext Chao Peng
2022-01-18 13:21 ` [PATCH v4 07/12] KVM: Add KVM_EXIT_MEMORY_ERROR exit Chao Peng
2022-01-18 13:21 ` [PATCH v4 08/12] KVM: Use memfile_pfn_ops to obtain pfn for private pages Chao Peng
2022-01-18 13:21 ` [PATCH v4 09/12] KVM: Handle page fault for private memory Chao Peng
2022-01-18 13:21 ` [PATCH v4 10/12] KVM: Register private memslot to memory backing store Chao Peng
2022-01-18 13:21 ` [PATCH v4 11/12] KVM: Zap existing KVM mappings when pages changed in the private fd Chao Peng
2022-01-18 13:21 ` [PATCH v4 12/12] KVM: Expose KVM_MEM_PRIVATE Chao Peng
2022-01-25 20:20   ` Maciej S. Szmigiero
2022-02-17 13:45     ` Chao Peng
2022-02-22  1:16       ` Maciej S. Szmigiero
2022-02-23 12:00         ` Chao Peng
2022-02-23 18:32           ` Maciej S. Szmigiero
2022-02-24  8:07             ` Chao Peng
2022-01-28 16:47 ` [PATCH v4 00/12] KVM: mm: fd-based approach for supporting KVM guest private memory Steven Price
2022-02-02  2:28   ` Nakajima, Jun
2022-02-02  9:23     ` Steven Price
2022-02-02 20:47       ` Nakajima, Jun
2022-02-08 18:33 ` Mike Rapoport
2022-02-17 13:47   ` Chao Peng

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=20220217130631.GB32679@chaop.bj.intel.com \
    --to=chao.p.peng@linux.intel.com \
    --cc=ak@linux.intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=bfields@fieldses.org \
    --cc=bp@alien8.de \
    --cc=corbet@lwn.net \
    --cc=dave.hansen@intel.com \
    --cc=david@redhat.com \
    --cc=hpa@zytor.com \
    --cc=hughd@google.com \
    --cc=jlayton@kernel.org \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=jun.nakajima@intel.com \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=luto@kernel.org \
    --cc=mingo@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=qemu-devel@nongnu.org \
    --cc=seanjc@google.com \
    --cc=tglx@linutronix.de \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    --cc=x86@kernel.org \
    --cc=yu.c.zhang@linux.intel.com \
    /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).