Re: [PATCH 3/4] kvm: powerpc: define a linux pte lookup function

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Bharat Bhushan <r65777@freescale.com> writes:

> 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@freescale.com>
> ---
>  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;
> +		}

What if we find a THP page that is splitting ?  Older function returned
__pte(0) in that case.


> +	}
> +
> +	/* If pte is not present return None */
> +	if (unlikely(!(pte & _PAGE_PRESENT)))
> +		return __pte(0);
> +
> +	return pte;
> +}
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* __KERNEL__ */
> -- 

-aneesh