Re: [PATCH 2/2] powerpc/mm/autonuma: Switch ppc64 to its own implementeation of saved write

[Aneesh Kumar K.V]

On Thursday 16 February 2017 03:16 AM, Andrew Morton wrote:
> On Thu,  9 Feb 2017 08:30:59 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
>
> > With this our protnone becomes a present pte with READ/WRITE/EXEC bit cleared.
> > By default we also set _PAGE_PRIVILEGED on such pte. This is now used to help
> > us identify a protnone pte that as saved write bit. For such pte, we will clear
> > the _PAGE_PRIVILEGED bit. The pte still remain non-accessible from both user
> > and kernel.
> I don't see how these patches differ from the ones which are presently
> in -mm.
>
> It helps to have a [0/n] email for a patch series and to put a version
> number in there as well.
>
> > +#define pte_mk_savedwrite pte_mk_savedwrite
> > +static inline pte_t pte_mk_savedwrite(pte_t pte)
> > +{
> > +	/*
> > +	 * Used by Autonuma subsystem to preserve the write bit
> > +	 * while marking the pte PROT_NONE. Only allow this
> > +	 * on PROT_NONE pte
> > +	 */
> > +	VM_BUG_ON((pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_RWX | _PAGE_PRIVILEGED)) !=
> > +		  cpu_to_be64(_PAGE_PRESENT | _PAGE_PRIVILEGED));
> > +	return __pte(pte_val(pte) & ~_PAGE_PRIVILEGED);
> > +}
> > +
> > +#define pte_savedwrite pte_savedwrite
> > +static inline bool pte_savedwrite(pte_t pte)
> > +{
> > +	/*
> > +	 * Saved write ptes are prot none ptes that doesn't have
> > +	 * privileged bit sit. We mark prot none as one which has
> > +	 * present and pviliged bit set and RWX cleared. To mark
> > +	 * protnone which used to have _PAGE_WRITE set we clear
> > +	 * the privileged bit.
> > +	 */
> > +	return !(pte_raw(pte) & cpu_to_be64(_PAGE_RWX | _PAGE_PRIVILEGED));
> > +}
> > +
> >   static inline pte_t pte_mkdevmap(pte_t pte)
> >   {
> >   	return __pte(pte_val(pte) | _PAGE_SPECIAL|_PAGE_DEVMAP);
> arch/powerpc/include/asm/book3s/64/pgtable.h doesn't have
> pte_mkdevmap().  What tree are you patching here?

I did post a V2 of this for which you replied
https://lkml.kernel.org/r/20170214162008.bd592c747fc5e167c10ce7b8@xxxxxxxxxxxxxxxxxxxx

I actually found the issue with this patch. I will be sending V3 after 
more testing.

-aneesh