From: Paolo Bonzini <pbonzini@redhat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Chao Peng <chao.p.peng@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Andy Lutomirski <luto@kernel.org>,
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>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Borislav Petkov <bp@alien8.de>,
Andrew Morton <akpm@linux-foundation.org>,
Joerg Roedel <jroedel@suse.de>, Andi Kleen <ak@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Vlastimil Babka <vbabka@suse.cz>,
Tom Lendacky <thomas.lendacky@amd.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Varad Gautam <varad.gautam@suse.com>,
Dario Faggioli <dfaggioli@suse.com>,
x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
Dave Hansen <dave.hansen@intel.com>,
Yu Zhang <yu.c.zhang@linux.intel.com>
Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory
Date: Thu, 16 Sep 2021 11:24:05 +0200 [thread overview]
Message-ID: <179fdb45-d8a4-9567-edfe-2168794f599e@redhat.com> (raw)
In-Reply-To: <20210915141147.s4mgtcfv3ber5fnt@black.fi.intel.com>
On 15/09/21 16:11, Kirill A. Shutemov wrote:
>> Would introducing memfd_unregister_guest() fix this?
> I considered this, but it get complex quickly.
>
> At what point it gets called? On KVM memslot destroy?
>
> What if multiple KVM slot share the same memfd? Add refcount into memfd on
> how many times the owner registered the memfd?
You will always have multiple KVM slots sharing the same memfd, because
memslots are SRCU-protected. So there will be multiple generations of
memslots around and unregistering must be delayed to after
synchronize_srcu (around the call to kvm_arch_commit_memory_region).
So KVM could just call memfd_{,un}register_guest as many times as it
calls fdget/fput. Looking at your test device, it would be like the
following pseudo-patch:
case GUEST_MEM_REGISTER: {
struct fd memfd = fdget(arg);
memfd_file = memfd.file;
return memfd_register_guest(memfd_file->f_inode, file,
&guest_ops, &guest_mem_ops);
}
case GUEST_MEM_UNREGISTER: {
if (!memfd_file)
return -EINVAL;
+ memfd_unregister_guest(memfd_file->f_inode, file);
fput(memfd_file);
memfd_file = NULL;
guest_mem_ops = NULL;
return 0;
and shmem_unregister_guest would be something like
struct shmem_inode_info *info = SHMEM_I(inode);
if (WARN_ON_ONCE(info->guest_owner != owner))
return;
if (--info->guest_usage_count)
return;
info->guest_owner = NULL;
info->guest_ops = NULL;
Paolo
> It would leave us in strange state: memfd refcount owners (struct KVM) and
> KVM memslot pins the struct file. Weird refcount exchnage program.
prev parent reply other threads:[~2021-09-16 9:24 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 0:52 [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory Sean Christopherson
2021-08-24 10:48 ` Yu Zhang
2021-08-26 0:35 ` Sean Christopherson
2021-08-26 13:23 ` Yu Zhang
2021-08-26 10:15 ` David Hildenbrand
2021-08-26 17:05 ` Andy Lutomirski
2021-08-26 21:26 ` David Hildenbrand
2021-08-27 18:24 ` Andy Lutomirski
2021-08-27 22:28 ` Sean Christopherson
2021-08-31 19:12 ` David Hildenbrand
2021-08-31 20:45 ` Sean Christopherson
2021-09-01 7:51 ` David Hildenbrand
2021-08-27 2:31 ` Yu Zhang
2021-08-31 19:08 ` David Hildenbrand
2021-08-31 20:01 ` Andi Kleen
2021-08-31 20:15 ` David Hildenbrand
2021-08-31 20:39 ` Andi Kleen
2021-09-01 3:34 ` Yu Zhang
2021-09-01 4:53 ` Andy Lutomirski
2021-09-01 7:12 ` Tian, Kevin
2021-09-01 10:24 ` Yu Zhang
2021-09-01 16:07 ` Andy Lutomirski
2021-09-01 16:27 ` David Hildenbrand
2021-09-02 8:34 ` Yu Zhang
2021-09-02 8:44 ` David Hildenbrand
2021-09-02 11:02 ` Yu Zhang
2021-09-02 8:19 ` Yu Zhang
2021-09-02 18:41 ` Andy Lutomirski
2021-09-07 1:33 ` Yan Zhao
2021-09-02 9:27 ` Joerg Roedel
2021-09-02 18:41 ` Andy Lutomirski
2021-09-02 18:57 ` Sean Christopherson
2021-09-02 19:07 ` Dave Hansen
2021-09-02 20:42 ` Andy Lutomirski
2021-08-27 22:18 ` Sean Christopherson
2021-08-31 19:07 ` David Hildenbrand
2021-08-31 21:54 ` Sean Christopherson
2021-09-01 8:09 ` David Hildenbrand
2021-09-01 15:54 ` Andy Lutomirski
2021-09-01 16:16 ` David Hildenbrand
2021-09-01 17:09 ` Andy Lutomirski
2021-09-01 16:18 ` James Bottomley
2021-09-01 16:22 ` David Hildenbrand
2021-09-01 16:31 ` James Bottomley
2021-09-01 16:37 ` David Hildenbrand
2021-09-01 16:45 ` James Bottomley
2021-09-01 17:08 ` David Hildenbrand
2021-09-01 17:50 ` Sean Christopherson
2021-09-01 17:53 ` David Hildenbrand
2021-09-01 17:08 ` Andy Lutomirski
2021-09-01 17:13 ` James Bottomley
2021-09-02 10:18 ` Joerg Roedel
2021-09-01 18:24 ` Andy Lutomirski
2021-09-01 19:26 ` Dave Hansen
2021-09-07 15:00 ` Tom Lendacky
2021-09-01 4:58 ` Andy Lutomirski
2021-09-01 7:49 ` David Hildenbrand
2021-09-02 18:47 ` Kirill A. Shutemov
2021-09-02 20:33 ` Sean Christopherson
2021-09-03 19:14 ` Kirill A. Shutemov
2021-09-03 19:15 ` Andy Lutomirski
2021-09-10 17:18 ` Kirill A. Shutemov
2021-09-15 19:58 ` Chao Peng
2021-09-15 13:51 ` David Hildenbrand
2021-09-15 14:29 ` Kirill A. Shutemov
2021-09-15 14:59 ` David Hildenbrand
2021-09-15 15:35 ` David Hildenbrand
2021-09-15 20:04 ` Kirill A. Shutemov
2021-09-15 14:11 ` Kirill A. Shutemov
2021-09-16 7:36 ` Chao Peng
2021-09-16 9:24 ` Paolo Bonzini [this message]
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