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

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Message-ID: <xv5qg4hfqvqzooounx57hzl4jzmfefitf3qklcdqzz7a4dufxn@v3r47r7p6ono>
Date: Thu, 26 Sep 2024 08:52:32 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Vlastimil Babka <vbabka@...e.cz>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>, 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 Thu, Sep 26, 2024 at 04:10:19PM GMT, 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: Shakeel Butt <shakeel.butt@...ux.dev>

> ---
> v3:
> * Avoid introducing PR_MADV_SELF and defer a non-pidfd version until later.

Seems like a good plan to decouple this patch from PR_MADV_SELF vs
PIDFD_SELF decision. I am hoping to see the follow up patch as well.

thanks,
Shakeel