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Date:   Mon, 11 Apr 2022 18:34:33 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     Sean Christopherson <seanjc@google.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-api@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@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>,
        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, david@redhat.com
Subject: Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory
 against RLIMIT_MEMLOCK
Message-ID: <20220411153433.6sqqqd6vzhyfjee6@box.shutemov.name>
References: <20220310140911.50924-1-chao.p.peng@linux.intel.com>
 <20220310140911.50924-5-chao.p.peng@linux.intel.com>
 <Yk8L0CwKpTrv3Rg3@google.com>
 <20220408130254.GB57095@chaop.bj.intel.com>
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On Fri, Apr 08, 2022 at 09:02:54PM +0800, Chao Peng wrote:
> > I think the correct approach is to not do the locking automatically for SHM_F_INACCESSIBLE,
> > and instead require userspace to do shmctl(.., SHM_LOCK, ...) if userspace knows the
> > consumers don't support migrate/swap.  That'd require wrapping migrate_page() and then
> > wiring up notifier hooks for migrate/swap, but IMO that's a good thing to get sorted
> > out sooner than later.  KVM isn't planning on support migrate/swap for TDX or SNP,
> > but supporting at least migrate for a software-only implementation a la pKVM should
> > be relatively straightforward.  On the notifiee side, KVM can terminate the VM if it
> > gets an unexpected migrate/swap, e.g. so that TDX/SEV VMs don't die later with
> > exceptions and/or data corruption (pre-SNP SEV guests) in the guest.
> 
> SHM_LOCK sounds like a good match.

Emm, no. shmctl(2) and SHM_LOCK are SysV IPC thing. I don't see how they
fit here.

-- 
 Kirill A. Shutemov