linux-kernel - Re: [PATCH v6 4/4] powerpc: Book3S 64-bit "heavyweight" KASAN support

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Date:   Wed, 12 Feb 2020 11:35:40 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        kasan-dev@...glegroups.com, aneesh.kumar@...ux.ibm.com,
        bsingharora@...il.com
Cc:     Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v6 4/4] powerpc: Book3S 64-bit "heavyweight" KASAN support



Le 12/02/2020 à 11:12, Daniel Axtens a écrit :
> Christophe Leroy <christophe.leroy@....fr> writes:
> 
>> Le 12/02/2020 à 06:47, Daniel Axtens a écrit :
>>> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
>>> index fbff9ff9032e..2911fdd3a6a0 100644
>>> --- a/arch/powerpc/include/asm/kasan.h
>>> +++ b/arch/powerpc/include/asm/kasan.h
>>> @@ -2,6 +2,8 @@
>>>    #ifndef __ASM_KASAN_H
>>>    #define __ASM_KASAN_H
>>>    
>>> +#include <asm/page.h>
>>> +
>>>    #ifdef CONFIG_KASAN
>>>    #define _GLOBAL_KASAN(fn)	_GLOBAL(__##fn)
>>>    #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(__##fn)
>>> @@ -14,29 +16,41 @@
>>>    
>>>    #ifndef __ASSEMBLY__
>>>    
>>> -#include <asm/page.h>
>>> -
>>>    #define KASAN_SHADOW_SCALE_SHIFT	3
>>>    
>>>    #define KASAN_SHADOW_START	(KASAN_SHADOW_OFFSET + \
>>>    				 (PAGE_OFFSET >> KASAN_SHADOW_SCALE_SHIFT))
>>>    
>>> +#ifdef CONFIG_KASAN_SHADOW_OFFSET
>>>    #define KASAN_SHADOW_OFFSET	ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET)
>>> +#endif
>>>    
>>> +#ifdef CONFIG_PPC32
>>>    #define KASAN_SHADOW_END	0UL
>>>    
>>> -#define KASAN_SHADOW_SIZE	(KASAN_SHADOW_END - KASAN_SHADOW_START)
>>> +#ifdef CONFIG_KASAN
>>> +void kasan_late_init(void);
>>> +#else
>>> +static inline void kasan_late_init(void) { }
>>> +#endif
>>> +
>>> +#endif
>>> +
>>> +#ifdef CONFIG_PPC_BOOK3S_64
>>> +#define KASAN_SHADOW_END	(KASAN_SHADOW_OFFSET + \
>>> +				 (RADIX_VMEMMAP_END >> KASAN_SHADOW_SCALE_SHIFT))
>>> +
>>> +static inline void kasan_late_init(void) { }
>>> +#endif
>>>    
>>>    #ifdef CONFIG_KASAN
>>>    void kasan_early_init(void);
>>>    void kasan_mmu_init(void);
>>>    void kasan_init(void);
>>> -void kasan_late_init(void);
>>>    #else
>>>    static inline void kasan_init(void) { }
>>>    static inline void kasan_mmu_init(void) { }
>>> -static inline void kasan_late_init(void) { }
>>>    #endif
>>
>> Why modify all this kasan_late_init() stuff ?
>>
>> This function is only called from kasan init_32.c, it is never called by
>> PPC64, so you should not need to modify anything at all.
> 
> I got a compile error for a missing symbol. I'll repro it and attach it.
> 

Oops, sorry. I looked too quickly. It is defined in kasan_init_32.c and 
called from mm/mem.c

We don't have a performance issue here, since this is called only once 
during startup. Could you define an empty kasan_late_init() in 
init_book3s_64.c instead ?

Christophe