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Message-ID: <93851312-6443-31ec-c194-8117e483f5d4@suse.cz>
Date:   Wed, 23 Mar 2022 14:19:29 +0100
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Subject: Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON
 with HW_TAGS
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To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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>
References: <cover.1643047180.git.andreyknvl@google.com>
 <44e5738a584c11801b2b8f1231898918efc8634a.1643047180.git.andreyknvl@google.com>
 <63704e10-18cf-9a82-cffb-052c6046ba7d@suse.cz>
 <YjsaaQo5pqmGdBaY@linutronix.de>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <YjsaaQo5pqmGdBaY@linutronix.de>
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On 3/23/22 14:02, Sebastian Andrzej Siewior wrote:
> 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

Hm but already this patch makes gfp_allowed_mask to be 0x1ffffff (thus
not covering 0x2000000u) when CONFIG_LOCKDEP is enabled and the KASAN
stuff not? 0x8000000u is just even further away.

> 	("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
>