Subject: Re: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

From: Michael Ellerman <[email-masked]>
Date: Tue, 02 Jun 2020 20:25:48 +1000

Christophe Leroy <[email-masked]> writes:
> 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 ?

Yes.

  powerpc/32: Disable KASAN with pages bigger than 16k
  
  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 128MB starting at 0xf8000000.
  With 4k pages, a PGD entry is 4MB
  With 16k pages, a PGD entry is 64MB
  With 64k pages, a PGD entry is 1GB which is too big.
  
  Until we rework the early shadow mapping, disable KASAN when the page
  size is too big.

  Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
  Cc: [email-masked] # v5.2+
  Reported-by: kbuild test robot <[email-masked]>
  Signed-off-by: Christophe Leroy <[email-masked]>
  Signed-off-by: Michael Ellerman <[email-masked]>
  Link: https://lore.kernel.org/r/7195fcde[email-masked]

cheers