linux-kernel - Re: [PATCH] mm/mincore: allow for making sys

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Date:   Sat, 5 Jan 2019 15:28:19 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

On Sat, Jan 5, 2019 at 3:16 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> It goes back to forever, it looks like. I can't find a reason.

Our man-pages talk abouit the "without doing IO" part. That may be the
result of our code, though, not the reason for it.

The BSD man-page has other flags, but doesn't describe what "in core"
really means:

     MINCORE_INCORE        Page is in core (resident).

     MINCORE_REFERENCED        Page has been referenced by us.

     MINCORE_MODIFIED        Page has been modified by us.

     MINCORE_REFERENCED_OTHER  Page has been referenced.

     MINCORE_MODIFIED_OTHER    Page has been modified.

     MINCORE_SUPER        Page is part of a large (``super'') page.

but the fact that it has MINCORE_MODIFIED_OTHER does obviously imply
that yes, historically it really did look up the pages elsewhere, not
just in the page tables.

Still, maybe we can get away with just making it be about our own page
tables. That would be lovely.

                 Linus