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Date:   Thu, 14 Jul 2022 06:15:26 +0200
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Subject: Re: [PATCH v7 04/14] mm/shmem: Support memfile_notifier
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To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     kvm@vger.kernel.org, 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, linux-kselftest@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>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
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        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, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>
References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com>
 <20220706082016.2603916-5-chao.p.peng@linux.intel.com>
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 <74097857-1908-2ff2-1e54-bf7e658ea6c6@amd.com>
 <20220713234903.GA2881285@chaop.bj.intel.com>
From:   "Gupta, Pankaj" <pankaj.gupta@amd.com>
In-Reply-To: <20220713234903.GA2881285@chaop.bj.intel.com>
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>>>>> +#ifdef CONFIG_MIGRATION
>>>>> +static int shmem_migrate_page(struct address_space *mapping,
>>>>> +			      struct page *newpage, struct page *page,
>>>>> +			      enum migrate_mode mode)
>>>>> +{
>>>>> +	struct inode *inode = mapping->host;
>>>>> +	struct shmem_inode_info *info = SHMEM_I(inode);
>>>>> +
>>>>> +	if (info->memfile_node.flags & MEMFILE_F_UNMOVABLE)
>>>>> +		return -EOPNOTSUPP;
>>>>> +	return migrate_page(mapping, newpage, page, mode);
>>>>
>>>> Wondering how well page migrate would work for private pages
>>>> on shmem memfd based backend?
>>>
>>>   From high level:
>>>     - KVM unset MEMFILE_F_UNMOVABLE bit to indicate it capable of
>>>       migrating a page.
>>>     - Introduce new 'migrate' callback(s) to memfile_notifier_ops for KVM
>>>       to register.
>>>     - The callback is hooked to migrate_page() here.
>>>     - Once page migration requested, shmem calls into the 'migrate'
>>>       callback(s) to perform additional steps for encrypted memory (For
>>>       TDX we will call TDH.MEM.PAGE.RELOCATE).
>>
>> Yes, that would require additional (protocol specific) handling for private
>> pages. Was trying to find where "MEMFILE_F_UNMOVABLE" flag is set currently?
> 
> It's set with memfile_register_notifier() in patch 13.

o.k.

Thanks,

Pankaj