linux-kernel - Re: [PATCH v3] mm/madvise: unrestrict process

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Message-ID: <c96c4cf6-e007-4a19-a830-4a2a073620e7@suse.cz>
Date: Fri, 27 Sep 2024 10:12:33 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Suren Baghdasaryan <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>,
 Shakeel Butt <shakeel.butt@...ux.dev>, linux-api@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Minchan Kim <minchan@...nel.org>, Christian Brauner <brauner@...nel.org>,
 pedro.falcato@...il.com
Subject: Re: [PATCH v3] mm/madvise: unrestrict process_madvise() for current
 process

On 9/26/24 17:10, Lorenzo Stoakes wrote:
> The process_madvise() call was introduced in commit ecb8ac8b1f14
> ("mm/madvise: introduce process_madvise() syscall: an external memory
> hinting API") as a means of performing madvise() operations on another
> process.
> 
> However, as it provides the means by which to perform multiple madvise()
> operations in a batch via an iovec, it is useful to utilise the same
> interface for performing operations on the current process rather than a
> remote one.
> 
> Commit 22af8caff7d1 ("mm/madvise: process_madvise() drop capability check
> if same mm") removed the need for a caller invoking process_madvise() on
> its own pidfd to possess the CAP_SYS_NICE capability, however this leaves
> the restrictions on operation in place.
> 
> Resolve this by only applying the restriction on operations when accessing
> a remote process.
> 
> Moving forward we plan to implement a simpler means of specifying this
> condition other than needing to establish a self pidfd, perhaps in the form
> of a sentinel pidfd.
> 
> Also take the opportunity to refactor the system call implementation
> abstracting the vectorised operation.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Looks like the destructive modes should work with the vectorized version
too, and with how it returns a partial success.

We'll need a man page update though, right?