linux-kernel - Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

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Date:   Thu, 13 Apr 2023 17:22:12 +0000
From:   Ackerley Tng <ackerleytng@...gle.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,
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Subject: Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to
 create restricted user memory

Chao Peng <chao.p.peng@...ux.intel.com> writes:

> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

> Introduce 'memfd_restricted' system call with the ability to create
> memory areas that are restricted from userspace access through ordinary
> MMU operations (e.g. read/write/mmap). The memory content is expected to
> be used through the new in-kernel interface by a third kernel module.

> ...

> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> new file mode 100644
> index 000000000000..56953c204e5c
> --- /dev/null
> +++ b/mm/restrictedmem.c
> @@ -0,0 +1,318 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/syscalls.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +#include <linux/restrictedmem.h>
> +
> +struct restrictedmem_data {
> +	struct mutex lock;
> +	struct file *memfd;

Can this be renamed to file, or lower_file (as in stacking filesystems)?

It's a little confusing because this pointer doesn't actually refer to
an fd.

'memfd' is already used by udmabuf to refer to an actual fd [1], which
makes this a little misleading.

[1]  
https://elixir.bootlin.com/linux/v6.2.10/source/tools/testing/selftests/drivers/dma-buf/udmabuf.c#L63

> +	struct list_head notifiers;
> +};
> +
> ...