On 7/21/19 8:58 AM, Bharath Vedartham wrote:
> *pte_lookup functions get the physical address for a given virtual
> address by getting a physical page using gup and use page_to_phys to get
> the physical address.
>
> Currently, atomic_pte_lookup manually walks the page tables. If this
> function fails to get a physical page, it will fall back too
> non_atomic_pte_lookup to get a physical page which uses the slow gup
> path to get the physical page.
>
> Instead of manually walking the page tables use __get_user_pages_fast
> which does the same thing and it does not fall back to the slow gup
> path.
>
> This is largely inspired from kvm code. kvm uses __get_user_pages_fast
> in hva_to_pfn_fast function which can run in an atomic context.
>
> Cc: Ira Weiny <ira.we...@intel.com>
> Cc: John Hubbard <jhubb...@nvidia.com>
> Cc: Jérôme Glisse <jgli...@redhat.com>
> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> Cc: Dimitri Sivanich <sivan...@sgi.com>
> Cc: Arnd Bergmann <a...@arndb.de>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux...@kvack.org
> Signed-off-by: Bharath Vedartham <linux.b...@gmail.com>
> ---
> drivers/misc/sgi-gru/grufault.c | 39 +++++----------------------------------
> 1 file changed, 5 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index 75108d2..121c9a4 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -202,46 +202,17 @@ static int non_atomic_pte_lookup(struct vm_area_struct
> *vma,
> static int atomic_pte_lookup(struct vm_area_struct *vma, unsigned long vaddr,
> int write, unsigned long *paddr, int *pageshift)
> {
> - pgd_t *pgdp;
> - p4d_t *p4dp;
> - pud_t *pudp;
> - pmd_t *pmdp;
> - pte_t pte;
> -
> - pgdp = pgd_offset(vma->vm_mm, vaddr);
> - if (unlikely(pgd_none(*pgdp)))
> - goto err;
> -
> - p4dp = p4d_offset(pgdp, vaddr);
> - if (unlikely(p4d_none(*p4dp)))
> - goto err;
> -
> - pudp = pud_offset(p4dp, vaddr);
> - if (unlikely(pud_none(*pudp)))
> - goto err;
> + struct page *page;
>
> - pmdp = pmd_offset(pudp, vaddr);
> - if (unlikely(pmd_none(*pmdp)))
> - goto err;
> -#ifdef CONFIG_X86_64
> - if (unlikely(pmd_large(*pmdp)))
> - pte = *(pte_t *) pmdp;
> - else
> -#endif
> - pte = *pte_offset_kernel(pmdp, vaddr);
> + *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
>
> - if (unlikely(!pte_present(pte) ||
> - (write && (!pte_write(pte) || !pte_dirty(pte)))))
> + if (!__get_user_pages_fast(vaddr, 1, write, &page))
> return 1;
Let's please use numeric, not boolean comparison, for the return value of
gup.
Also, optional: as long as you're there, atomic_pte_lookup() ought to
either return a bool (true == success) or an errno, rather than a
numeric zero or one.
Other than that, this looks like a good cleanup, I wonder how many
open-coded gup implementations are floating around like this.
thanks,
--
John Hubbard
NVIDIA
>
> - *paddr = pte_pfn(pte) << PAGE_SHIFT;
> -
> - *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> + *paddr = page_to_phys(page);
> + put_user_page(page);
>
> return 0;
> -
> -err:
> - return 1;
> }
>
> static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>
