On Wed, 2013-10-09 at 03:48 -0500, Bhushan Bharat-R65777 wrote:
>
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, October 09, 2013 3:07 AM
> > To: Bhushan Bharat-R65777
> > Cc: agraf@xxxxxxx; Yoder Stuart-B08248; kvm@xxxxxxxxxxxxxxx; kvm-
> > ppc@xxxxxxxxxxxxxxx; paulus@xxxxxxxxx; Bhushan Bharat-R65777
> > Subject: Re: [PATCH 3/4] kvm: powerpc: define a linux pte lookup function
> >
> > On Tue, 2013-10-08 at 11:33 +0530, Bharat Bhushan wrote:
> > > We need to search linux "pte" to get "pte" attributes for setting TLB
> > > in KVM.
> > > This patch defines a linux_pte_lookup() function for same.
> > >
> > > Signed-off-by: Bharat Bhushan <bharat.bhushan@xxxxxxxxxxxxx>
> > > ---
> > > arch/powerpc/include/asm/pgtable.h | 35 +++++++++++++++++++++++++++++++++++
> > > 1 files changed, 35 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/arch/powerpc/include/asm/pgtable.h
> > > b/arch/powerpc/include/asm/pgtable.h
> > > index 7d6eacf..fd26c04 100644
> > > --- a/arch/powerpc/include/asm/pgtable.h
> > > +++ b/arch/powerpc/include/asm/pgtable.h
> > > @@ -223,6 +223,41 @@ extern int gup_hugepte(pte_t *ptep, unsigned long
> > > sz, unsigned long addr, #endif pte_t
> > > *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
> > > unsigned *shift);
> > > +
> > > +static inline pte_t lookup_linux_pte(pgd_t *pgdir, unsigned long hva,
> > > + unsigned long *pte_sizep)
> > > +{
> > > + pte_t *ptep;
> > > + pte_t pte;
> > > + unsigned long ps = *pte_sizep;
> > > + unsigned int shift;
> > > +
> > > + ptep = find_linux_pte_or_hugepte(pgdir, hva, &shift);
> > > + if (!ptep)
> > > + return __pte(0);
> > > + if (shift)
> > > + *pte_sizep = 1ul << shift;
> > > + else
> > > + *pte_sizep = PAGE_SIZE;
> > > +
> > > + if (ps > *pte_sizep)
> > > + return __pte(0);
> > > +
> > > + /* wait until _PAGE_BUSY is clear */
> > > + while (1) {
> > > + pte = pte_val(*ptep);
> > > + if (unlikely(pte & _PAGE_BUSY)) {
> > > + cpu_relax();
> > > + continue;
> > > + }
> > > + }
> > > +
> > > + /* If pte is not present return None */
> > > + if (unlikely(!(pte & _PAGE_PRESENT)))
> > > + return __pte(0);
> > > +
> > > + return pte;
> > > +}
> >
> > Can lookup_linux_pte_and_update() call lookup_linux_pte()?
>
> What lookup_linux_pte_and_update() does:-
> - find_linux_pte_or_hugepte()
> - does size and some other trivial checks
> - Then atomically update the pte:-
> => while()
> => wait till _PAGE_BUSY is clear
> => atomically update the pte
> => if not updated then go back to while() above else break
>
>
> While what lookup_linux_pte() does:-
> - find_linux_pte_or_hugepte()
> - does size and some other trivial checks
> - wait till _PAGE_BUSY is clear
> - return pte
>
> I am finding it difficult to call lookup_linux_pte() from lookup_linux_pte_and_update().
You could factor out a common lookup_linux_ptep().
-Scott
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