linux-kernel - Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW

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Message-ID: <YjsaaQo5pqmGdBaY@linutronix.de>
Date:   Wed, 23 Mar 2022 14:02:33 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     andrey.konovalov@...ux.dev,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON
 with HW_TAGS

On 2022-03-23 12:48:29 [+0100], Vlastimil Babka wrote:
> > +#ifdef CONFIG_KASAN_HW_TAGS
> >  #define ___GFP_SKIP_KASAN_POISON	0x1000000u
> > +#else
> > +#define ___GFP_SKIP_KASAN_POISON	0
> > +#endif
> >  #ifdef CONFIG_LOCKDEP
> >  #define ___GFP_NOLOCKDEP	0x2000000u
> >  #else
> > @@ -251,7 +255,9 @@ struct vm_area_struct;
> >  #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
> >  
> >  /* Room for N __GFP_FOO bits */
> > -#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))
> > +#define __GFP_BITS_SHIFT (24 +					\
> > +			  IS_ENABLED(CONFIG_KASAN_HW_TAGS) +	\
> > +			  IS_ENABLED(CONFIG_LOCKDEP))
> 
> This breaks __GFP_NOLOCKDEP, see:
> https://lore.kernel.org/all/YjoJ4CzB3yfWSV1F@linutronix.de/

This could work because ___GFP_NOLOCKDEP is still 0x2000000u. In
	("kasan, page_alloc: allow skipping memory init for HW_TAGS")
	https://lore.kernel.org/all/0d53efeff345de7d708e0baa0d8829167772521e.1643047180.git.andreyknvl@google.com/

This is replaced with 0x8000000u which breaks lockdep.

Sebastian