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From: Matthew Wilcox <willy@infradead.org>
To: Suren Baghdasaryan <surenb@google.com>
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Subject: Re: [PATCH v2 1/6] mm: introduce vma->vm_flags modifier functions
Date: Wed, 25 Jan 2023 18:37:36 +0000	[thread overview]
Message-ID: <Y9F28J9njAtwifuL@casper.infradead.org> (raw)
In-Reply-To: <CAJuCfpEcVCZaCGzc-Wim25eaV5e6YG1YJAAdKwZ6JHViB0z8aw@mail.gmail.com>

On Wed, Jan 25, 2023 at 08:49:50AM -0800, Suren Baghdasaryan wrote:
> On Wed, Jan 25, 2023 at 1:10 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > > +     /*
> > > +      * Flags, see mm.h.
> > > +      * WARNING! Do not modify directly.
> > > +      * Use {init|reset|set|clear|mod}_vm_flags() functions instead.
> > > +      */
> > > +     unsigned long vm_flags;
> >
> > We have __private and ACCESS_PRIVATE() to help with enforcing this.
> 
> Thanks for pointing this out, Peter! I guess for that I'll need to
> convert all read accesses and provide get_vm_flags() too? That will
> cause some additional churt (a quick search shows 801 hits over 248
> files) but maybe it's worth it? I think Michal suggested that too in
> another patch. Should I do that while we are at it?

Here's a trick I saw somewhere in the VFS:

	union {
		const vm_flags_t vm_flags;
		vm_flags_t __private __vm_flags;
	};

Now it can be read by anybody but written only by those using
ACCESS_PRIVATE.
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

  parent reply	other threads:[~2023-01-25 18:39 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20230125083851.27759-1-surenb@google.com>
     [not found] ` <20230125083851.27759-2-surenb@google.com>
2023-01-25  9:09   ` [PATCH v2 1/6] mm: introduce vma->vm_flags modifier functions Peter Zijlstra
     [not found]     ` <CAJuCfpEcVCZaCGzc-Wim25eaV5e6YG1YJAAdKwZ6JHViB0z8aw@mail.gmail.com>
2023-01-25 18:37       ` Matthew Wilcox [this message]
2023-01-25 18:33   ` Matthew Wilcox
     [not found]   ` <Y9JFFYjfJf9uDijE@kernel.org>
     [not found]     ` <Y9KTUw/04FmBVplw@kernel.org>
2023-01-26 15:09       ` Matthew Wilcox

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