linux-kernel - Re: [PATCH v7 04/14] mm/shmem: Support memfile

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Message-ID: <74097857-1908-2ff2-1e54-bf7e658ea6c6@amd.com>
Date:   Wed, 13 Jul 2022 12:01:13 +0200
From:   "Gupta, Pankaj" <pankaj.gupta@....com>
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, linux-kselftest@...r.kernel.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>,
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        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
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        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 04/14] mm/shmem: Support memfile_notifier


>>> +#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?

Thanks,
Pankaj