Re: [PATCH V3 5/8] x86: Introduce function to get pmd entry pointer

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Nov 11, 2014 at 06:43:43AM +0100, Juergen Gross wrote:
> Introduces lookup_pmd_address() to get the address of the pmd entry
> related to a virtual address in the current address space. This
> function is needed for support of a virtual mapped sparse p2m list
> in xen pv domains.
>
What is wrong with using 'lookup_address' ?
 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  arch/x86/include/asm/pgtable_types.h |  1 +
>  arch/x86/mm/pageattr.c               | 20 ++++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 0778964..d83f5e7 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -396,6 +396,7 @@ static inline void update_page_count(int level, unsigned long pages) { }
>  extern pte_t *lookup_address(unsigned long address, unsigned int *level);
>  extern pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
>  				    unsigned int *level);
> +extern pmd_t *lookup_pmd_address(unsigned long address);
>  extern phys_addr_t slow_virt_to_phys(void *__address);
>  extern int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
>  				   unsigned numpages, unsigned long page_flags);
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 36de293..1298108 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -384,6 +384,26 @@ static pte_t *_lookup_address_cpa(struct cpa_data *cpa, unsigned long address,
>  }
>  
>  /*
> + * Lookup the PMD entry for a virtual address. Return a pointer to the entry
> + * or NULL if not present.
> + */
> +pmd_t *lookup_pmd_address(unsigned long address)
> +{
> +	pgd_t *pgd;
> +	pud_t *pud;
> +
> +	pgd = pgd_offset_k(address);
> +	if (pgd_none(*pgd))
> +		return NULL;
> +
> +	pud = pud_offset(pgd, address);
> +	if (pud_none(*pud) || pud_large(*pud) || !pud_present(*pud))
> +		return NULL;
> +
> +	return pmd_offset(pud, address);
> +}
> +
> +/*
>   * This is necessary because __pa() does not work on some
>   * kinds of memory, like vmalloc() or the alloc_remap()
>   * areas on 32-bit NUMA systems.  The percpu areas can
> -- 
> 2.1.2
>