> -----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().
Thanks
-Bharat
>
> -Scott
>
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