Re: [PATCH] powerpc: fix ioremap_flags() with book3e pte definition

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

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.
> 
> Signed-off-by: Li Yang <leoli@freescale.com>
> ---
>  arch/powerpc/mm/pgtable_32.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> 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 &= ~(_PAGE_USER | _PAGE_EXEC);
>  
> +#if defined(CONFIG_FSL_BOOKE) && defined(CONFIG_PTE_64BIT)
> +	/* supervisor read permission has just been cleared, add back */
> +	flags |= _PAGE_BAP_SR;
> +#endif
> +

So this is a bit fishy indeed. pgtable_64.c seems to have the same
problem in fact.

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 ?

_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 ?

Cheers,
Ben.