Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 23 Mar 2022 14:02:33 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     andrey.konovalov@linux.dev,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON
 with HW_TAGS
Message-ID: <YjsaaQo5pqmGdBaY@linutronix.de>
References: <cover.1643047180.git.andreyknvl@google.com>
 <44e5738a584c11801b2b8f1231898918efc8634a.1643047180.git.andreyknvl@google.com>
 <63704e10-18cf-9a82-cffb-052c6046ba7d@suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <63704e10-18cf-9a82-cffb-052c6046ba7d@suse.cz>
Precedence: bulk

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