linux-kernel - Re: [PATCH 5/5] alloc_tag: config to store page allocation tag refs in page flags

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Message-Id: <20240819184649.8fc7da59f89290f716ae0553@linux-foundation.org>
Date: Mon, 19 Aug 2024 18:46:49 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, kent.overstreet@...ux.dev,
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Subject: Re: [PATCH 5/5] alloc_tag: config to store page allocation tag refs
 in page flags

On Mon, 19 Aug 2024 21:40:34 +0100 Matthew Wilcox <willy@...radead.org> wrote:

> On Mon, Aug 19, 2024 at 01:39:16PM -0700, Suren Baghdasaryan wrote:
> > On Mon, Aug 19, 2024 at 12:34 PM Matthew Wilcox <willy@...radead.org> wrote:
> > > So if ALLOC_TAG_REF_WIDTH is big enough, it's going to force last_cpupid
> > > into struct page.
> > 
> > Thanks for taking a look!
> > Yes, but how is this field different from say KASAN_TAG_WIDTH which
> > can also force last_cpupid out of page flags?
> 
> Because KASAN isn't for production use?
> 
> > >  That will misalign struct page and disable HVO -- with no warning!
> > 
> > mminit_verify_pageflags_layout already has a mminit_dprintk() to
> > indicate this condition. Is that not enough?
> 
> Fair.

Is a BUILD_BUG_ON() feasible here?