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Subject: Re: [PATCH] powerpc: fix ioremap_flags() with book3e pte definition
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From: Kumar Gala <galak@kernel.crashing.org>
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Date: Fri, 14 May 2010 12:57:11 -0500
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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On Feb 7, 2010, at 10:21 PM, Benjamin Herrenschmidt wrote:

> On Fri, 2010-02-05 at 00:53 +0800, Li Yang wrote:
>> We can't just clear the user read permission in book3e pte, because
>> that will also clear supervisor read permission.  This surely isn't
>> desired.  Fix the problem by adding the supervisor read back.
>>=20
>> Signed-off-by: Li Yang <leoli@freescale.com>
>> ---
>> arch/powerpc/mm/pgtable_32.c |    5 +++++
>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>=20
>> diff --git a/arch/powerpc/mm/pgtable_32.c =
b/arch/powerpc/mm/pgtable_32.c
>> index cb96cb2..aff7c04 100644
>> --- a/arch/powerpc/mm/pgtable_32.c
>> +++ b/arch/powerpc/mm/pgtable_32.c
>> @@ -144,6 +144,11 @@ ioremap_flags(phys_addr_t addr, unsigned long =
size, unsigned long flags)
>> 	/* we don't want to let _PAGE_USER and _PAGE_EXEC leak out */
>> 	flags &=3D ~(_PAGE_USER | _PAGE_EXEC);
>>=20
>> +#if defined(CONFIG_FSL_BOOKE) && defined(CONFIG_PTE_64BIT)
>> +	/* supervisor read permission has just been cleared, add back */
>> +	flags |=3D _PAGE_BAP_SR;
>> +#endif
>> +
>=20
> So this is a bit fishy indeed. pgtable_64.c seems to have the same
> problem in fact.
>=20
> It boils down to the "hack" I have in the new PTE format which =
consists
> of having _SR be part of _PAGE_USER. I wonder if I should change that
> instead. Kumar, what do you reckon ?
>=20
> _Maybe_ an option is to have _PAGE_NO_USER that defaults to be
> ~_PAGE_USER in pte-common.h and can be set in pte-book3e.h to
> only strip out UR and UW ?

We never closed on this.  I think lets add _PAGE_NO_USER

- k=