linux-kernel - Re: [PATCH v8 8/8] KVM: Enable and expose KVM_MEM

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Date:   Tue, 4 Oct 2022 17:55:28 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>, wei.w.wang@...el.com
Subject: Re: [PATCH v8 8/8] KVM: Enable and expose KVM_MEM_PRIVATE

On Thu, Sep 15, 2022 at 10:29:13PM +0800, Chao Peng wrote:
> Expose KVM_MEM_PRIVATE and memslot fields private_fd/offset to
> userspace. KVM will register/unregister private memslot to fd-based
> memory backing store and response to invalidation event from
> inaccessible_notifier to zap the existing memory mappings in the
> secondary page table.
> 
> Whether KVM_MEM_PRIVATE is actually exposed to userspace is determined
> by architecture code which can turn on it by overriding the default
> kvm_arch_has_private_mem().
> 
> A 'kvm' reference is added in memslot structure since in
> inaccessible_notifier callback we can only obtain a memslot reference
> but 'kvm' is needed to do the zapping.
> 
> Co-developed-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>

ld: arch/x86/../../virt/kvm/kvm_main.o: in function `kvm_free_memslot':
kvm_main.c:(.text+0x1385): undefined reference to `inaccessible_unregister_notifier'
ld: arch/x86/../../virt/kvm/kvm_main.o: in function `kvm_set_memslot':
kvm_main.c:(.text+0x1b86): undefined reference to `inaccessible_register_notifier'
ld: kvm_main.c:(.text+0x1c85): undefined reference to `inaccessible_unregister_notifier'
ld: arch/x86/kvm/mmu/mmu.o: in function `kvm_faultin_pfn':
mmu.c:(.text+0x1e38): undefined reference to `inaccessible_get_pfn'
ld: arch/x86/kvm/mmu/mmu.o: in function `direct_page_fault':
mmu.c:(.text+0x67ca): undefined reference to `inaccessible_put_pfn'
make: *** [Makefile:1169: vmlinux] Error 1

I attached kernel config for reproduction.

The problem is that CONFIG_MEMFD_CREATE does not get enabled:

mm/Makefile:obj-$(CONFIG_MEMFD_CREATE) += memfd.o memfd_inaccessible.o

BR, Jarkko

View attachment "config" of type "text/plain" (45092 bytes)