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Subject: Re: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <7195fcde7314ccbf7a081b356084a69d421b10d4.1590660977.git.christophe.leroy@csgroup.eu>
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Date:   Sat, 30 May 2020 19:22:28 +0200
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Le 28/05/2020 à 12:17, Christophe Leroy a écrit :
> Mapping of early shadow area is implemented by using a single static
> page table having all entries pointing to the same early shadow page.
> The shadow area must therefore occupy full PGD entries.
> 
> The shadow area has a size of 128Mbytes starting at 0xf8000000.
> With 4k pages, a PGD entry is 4Mbytes
> With 16k pages, a PGD entry is 64Mbytes
> With 64k pages, a PGD entry is 256Mbytes which is too big.

That's for 32k pages that a PGD is 256Mbytes.

With 64k pages, a PGD entry is 1Gbytes which is too big.

Michael, can you fix the commit log ?

Thanks
Christophe

> 
> Until we rework the early shadow mapping, disable KASAN when the
> page size is too big.
> 
> Reported-by: kbuild test robot <lkp@intel.com>
> Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>   arch/powerpc/Kconfig | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1dfa59126fcf..066b36bf9efa 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -169,8 +169,8 @@ config PPC
>   	select HAVE_ARCH_AUDITSYSCALL
>   	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
>   	select HAVE_ARCH_JUMP_LABEL
> -	select HAVE_ARCH_KASAN			if PPC32
> -	select HAVE_ARCH_KASAN_VMALLOC		if PPC32
> +	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
> +	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
>   	select HAVE_ARCH_KGDB
>   	select HAVE_ARCH_MMAP_RND_BITS
>   	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
>