From: Andy Lutomirski <luto@kernel.org>
To: Chao Peng <chao.p.peng@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vishal Annapurve <vannapurve@google.com>,
Marc Orr <marcorr@google.com>, kvm list <kvm@vger.kernel.org>,
LKML <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, Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
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 <x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
Hugh Dickins <hughd@google.com>,
Jeff Layton <jlayton@kernel.org>,
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Andrew Morton <akpm@linux-foundation.org>,
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Steven Price <steven.price@arm.com>,
"Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
Vlastimil Babka <vbabka@suse.cz>,
Yu Zhang <yu.c.zhang@linux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Jun Nakajima <jun.nakajima@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andi Kleen <ak@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com,
Quentin Perret <qperret@google.com>,
Michael Roth <michael.roth@amd.com>,
mhocko@suse.com
Subject: Re: [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory
Date: Tue, 14 Jun 2022 10:37:37 -0700 [thread overview]
Message-ID: <CALCETrWw=Q=1AKW0Jcj3ZGscjyjDJXAjuxOnQx_sabQ6ZtS-wg@mail.gmail.com> (raw)
In-Reply-To: <20220614072800.GB1783435@chaop.bj.intel.com>
On Tue, Jun 14, 2022 at 12:32 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> On Thu, Jun 09, 2022 at 08:29:06PM +0000, Sean Christopherson wrote:
> > On Wed, Jun 08, 2022, Vishal Annapurve wrote:
> >
> > One argument is that userspace can simply rely on cgroups to detect misbehaving
> > guests, but (a) those types of OOMs will be a nightmare to debug and (b) an OOM
> > kill from the host is typically considered a _host_ issue and will be treated as
> > a missed SLO.
> >
> > An idea for handling this in the kernel without too much complexity would be to
> > add F_SEAL_FAULT_ALLOCATIONS (terrible name) that would prevent page faults from
> > allocating pages, i.e. holes can only be filled by an explicit fallocate(). Minor
> > faults, e.g. due to NUMA balancing stupidity, and major faults due to swap would
> > still work, but writes to previously unreserved/unallocated memory would get a
> > SIGSEGV on something it has mapped. That would allow the userspace VMM to prevent
> > unintentional allocations without having to coordinate unmapping/remapping across
> > multiple processes.
>
> Since this is mainly for shared memory and the motivation is catching
> misbehaved access, can we use mprotect(PROT_NONE) for this? We can mark
> those range backed by private fd as PROT_NONE during the conversion so
> subsequence misbehaved accesses will be blocked instead of causing double
> allocation silently.
This patch series is fairly close to implementing a rather more
efficient solution. I'm not familiar enough with hypervisor userspace
to really know if this would work, but:
What if shared guest memory could also be file-backed, either in the
same fd or with a second fd covering the shared portion of a memslot?
This would allow changes to the backing store (punching holes, etc) to
be some without mmap_lock or host-userspace TLB flushes? Depending on
what the guest is doing with its shared memory, userspace might need
the memory mapped or it might not.
--Andy
next prev parent reply other threads:[~2022-06-14 17:37 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 15:37 [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory Chao Peng
2022-05-19 15:37 ` [PATCH v6 1/8] mm: Introduce memfile_notifier Chao Peng
2022-05-19 15:37 ` [PATCH v6 2/8] mm/shmem: Support memfile_notifier Chao Peng
2022-05-19 15:37 ` [PATCH v6 3/8] mm/memfd: Introduce MFD_INACCESSIBLE flag Chao Peng
2022-05-31 19:15 ` Vishal Annapurve
2022-06-01 10:17 ` Chao Peng
2022-06-01 12:11 ` Gupta, Pankaj
2022-06-02 10:07 ` Chao Peng
2022-06-14 20:23 ` Sean Christopherson
2022-06-15 8:53 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 4/8] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-05-20 17:57 ` Andy Lutomirski
2022-05-20 18:31 ` Sean Christopherson
2022-05-22 4:03 ` Andy Lutomirski
2022-05-23 13:21 ` Chao Peng
2022-05-23 15:22 ` Sean Christopherson
2022-05-30 13:26 ` Chao Peng
2022-06-10 16:14 ` Sean Christopherson
2022-06-14 6:45 ` Chao Peng
2022-06-23 22:59 ` Michael Roth
2022-06-24 8:54 ` Chao Peng
2022-06-24 13:01 ` Michael Roth
2022-06-17 20:52 ` Sean Christopherson
2022-06-17 21:27 ` Sean Christopherson
2022-06-20 14:09 ` Chao Peng
2022-06-20 14:08 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 5/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-05-19 15:37 ` [PATCH v6 6/8] KVM: Handle page fault for private memory Chao Peng
2022-06-17 21:30 ` Sean Christopherson
2022-06-20 14:16 ` Chao Peng
2022-08-19 0:40 ` Kirill A. Shutemov
2022-08-25 23:43 ` Sean Christopherson
2022-06-24 3:58 ` Nikunj A. Dadhania
2022-06-24 9:02 ` Chao Peng
2022-06-30 19:14 ` Vishal Annapurve
2022-06-30 22:21 ` Michael Roth
2022-07-01 1:21 ` Xiaoyao Li
2022-07-07 20:08 ` Sean Christopherson
2022-07-08 3:29 ` Xiaoyao Li
2022-07-20 23:08 ` Vishal Annapurve
2022-07-21 9:45 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 7/8] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-06-23 22:07 ` Michael Roth
2022-06-24 8:43 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 8/8] memfd_create.2: Describe MFD_INACCESSIBLE flag Chao Peng
2022-06-06 20:09 ` [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory Vishal Annapurve
2022-06-07 6:57 ` Chao Peng
2022-06-08 0:55 ` Marc Orr
2022-06-08 2:18 ` Chao Peng
2022-06-08 19:37 ` Vishal Annapurve
2022-06-09 20:29 ` Sean Christopherson
2022-06-14 7:28 ` Chao Peng
2022-06-14 17:37 ` Andy Lutomirski [this message]
2022-06-14 19:08 ` Sean Christopherson
2022-06-14 20:59 ` Andy Lutomirski
2022-06-15 9:17 ` Chao Peng
2022-06-15 14:29 ` Sean Christopherson
2022-06-10 0:11 ` Marc Orr
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