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Date:   Tue, 29 Nov 2022 14:21:39 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Michael Roth <michael.roth@amd.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
        qemu-devel@nongnu.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>,
        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, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>, tabba@google.com,
        mhocko@suse.com, Muchun Song <songmuchun@bytedance.com>,
        wei.w.wang@intel.com
Subject: Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to
 create restricted user memory
Message-ID: <20221129112139.usp6dqhbih47qpjl@box.shutemov.name>
References: <20221025151344.3784230-1-chao.p.peng@linux.intel.com>
 <20221025151344.3784230-2-chao.p.peng@linux.intel.com>
 <20221129000632.sz6pobh6p7teouiu@amd.com>
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In-Reply-To: <20221129000632.sz6pobh6p7teouiu@amd.com>
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On Mon, Nov 28, 2022 at 06:06:32PM -0600, Michael Roth wrote:
> On Tue, Oct 25, 2022 at 11:13:37PM +0800, Chao Peng wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > 
> 
> <snip>
> 
> > +static struct file *restrictedmem_file_create(struct file *memfd)
> > +{
> > +	struct restrictedmem_data *data;
> > +	struct address_space *mapping;
> > +	struct inode *inode;
> > +	struct file *file;
> > +
> > +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> > +	if (!data)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	data->memfd = memfd;
> > +	mutex_init(&data->lock);
> > +	INIT_LIST_HEAD(&data->notifiers);
> > +
> > +	inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> > +	if (IS_ERR(inode)) {
> > +		kfree(data);
> > +		return ERR_CAST(inode);
> > +	}
> > +
> > +	inode->i_mode |= S_IFREG;
> > +	inode->i_op = &restrictedmem_iops;
> > +	inode->i_mapping->private_data = data;
> > +
> > +	file = alloc_file_pseudo(inode, restrictedmem_mnt,
> > +				 "restrictedmem", O_RDWR,
> > +				 &restrictedmem_fops);
> > +	if (IS_ERR(file)) {
> > +		iput(inode);
> > +		kfree(data);
> > +		return ERR_CAST(file);
> > +	}
> > +
> > +	file->f_flags |= O_LARGEFILE;
> > +
> > +	mapping = memfd->f_mapping;
> > +	mapping_set_unevictable(mapping);
> > +	mapping_set_gfp_mask(mapping,
> > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> 
> Is this supposed to prevent migration of pages being used for
> restrictedmem/shmem backend?

Yes, my bad. I expected it to prevent migration, but it is not true.

Looks like we need to bump refcount in restrictedmem_get_page() and reduce
it back when KVM is no longer use it.

Chao, could you adjust it?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov