Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW_TAGS

Vlastimil Babka
2022-03-23T13:21:04Z

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
>