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Date:   Sun, 18 Aug 2019 23:28:24 +0530
From:   Bharath Vedartham <linux.bhar@gmail.com>
To:     jhubbard@nvidia.com, gregkh@linuxfoundation.org, sivanich@sgi.com,
        arnd@arndb.de
Cc:     ira.weiny@intel.com, jglisse@redhat.com,
        william.kucharski@oracle.com, hch@lst.de,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees][PATCH v5 1/1] sgi-gru: Remove *pte_lookup
 functions, Convert to get_user_page*()
Message-ID: <20190818175824.GA6635@bharath12345-Inspiron-5559>
References: <1565379497-29266-1-git-send-email-linux.bhar@gmail.com>
 <1565379497-29266-2-git-send-email-linux.bhar@gmail.com>
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Hi Dimitri,

Can you confirm that this driver will run gru_vtop() in interrupt
context?

If so, I ll send you another set of patches in which I don't change the
*pte_lookup functions but only change put_page to put_user_page and
remove the ifdef for CONFIG_HUGETLB_PAGE.

Thank you for your time.

Thank you
Bharath

On Sat, Aug 10, 2019 at 01:08:17AM +0530, Bharath Vedartham wrote:
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page() or
> release_pages().
> 
> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
> 
> As part of this conversion, the *pte_lookup functions can be removed and
> be easily replaced with get_user_pages_fast() functions. In the case of
> atomic lookup, __get_user_pages_fast() is used, because it does not fall
> back to the slow path: get_user_pages(). get_user_pages_fast(), on the other
> hand, first calls __get_user_pages_fast(), but then falls back to the
> slow path if __get_user_pages_fast() fails.
> 
> Also: remove unnecessary CONFIG_HUGETLB ifdefs.
> 
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: J?r?me Glisse <jglisse@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Dimitri Sivanich <sivanich@sgi.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: William Kucharski <william.kucharski@oracle.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-kernel-mentees@lists.linuxfoundation.org
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
> Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> ---
> This is a fold of the 3 patches in the v2 patch series.
> The review tags were given to the individual patches.
> 
> Changes since v3
> 	- Used gup flags in get_user_pages_fast rather than
> 	boolean flags.
> Changes since v4
> 	- Updated changelog according to John Hubbard.
> ---
>  drivers/misc/sgi-gru/grufault.c | 112 +++++++++-------------------------------
>  1 file changed, 24 insertions(+), 88 deletions(-)
> 
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index 4b713a8..304e9c5 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -166,96 +166,20 @@ static void get_clear_fault_map(struct gru_state *gru,
>  }
>  
>  /*
> - * Atomic (interrupt context) & non-atomic (user context) functions to
> - * convert a vaddr into a physical address. The size of the page
> - * is returned in pageshift.
> - * 	returns:
> - * 		  0 - successful
> - * 		< 0 - error code
> - * 		  1 - (atomic only) try again in non-atomic context
> - */
> -static int non_atomic_pte_lookup(struct vm_area_struct *vma,
> -				 unsigned long vaddr, int write,
> -				 unsigned long *paddr, int *pageshift)
> -{
> -	struct page *page;
> -
> -#ifdef CONFIG_HUGETLB_PAGE
> -	*pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> -#else
> -	*pageshift = PAGE_SHIFT;
> -#endif
> -	if (get_user_pages(vaddr, 1, write ? FOLL_WRITE : 0, &page, NULL) <= 0)
> -		return -EFAULT;
> -	*paddr = page_to_phys(page);
> -	put_page(page);
> -	return 0;
> -}
> -
> -/*
> - * atomic_pte_lookup
> + * mmap_sem is already helod on entry to this function. This guarantees
> + * existence of the page tables.
>   *
> - * Convert a user virtual address to a physical address
>   * Only supports Intel large pages (2MB only) on x86_64.
> - *	ZZZ - hugepage support is incomplete
> - *
> - * NOTE: mmap_sem is already held on entry to this function. This
> - * guarantees existence of the page tables.
> + *	ZZZ - hugepage support is incomplete.
>   */
> -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;
> -
> -	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);
> -
> -	if (unlikely(!pte_present(pte) ||
> -		     (write && (!pte_write(pte) || !pte_dirty(pte)))))
> -		return 1;
> -
> -	*paddr = pte_pfn(pte) << PAGE_SHIFT;
> -#ifdef CONFIG_HUGETLB_PAGE
> -	*pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> -#else
> -	*pageshift = PAGE_SHIFT;
> -#endif
> -	return 0;
> -
> -err:
> -	return 1;
> -}
> -
>  static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  		    int write, int atomic, unsigned long *gpa, int *pageshift)
>  {
>  	struct mm_struct *mm = gts->ts_mm;
>  	struct vm_area_struct *vma;
>  	unsigned long paddr;
> -	int ret, ps;
> +	int ret;
> +	struct page *page;
>  
>  	vma = find_vma(mm, vaddr);
>  	if (!vma)
> @@ -263,21 +187,33 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  
>  	/*
>  	 * Atomic lookup is faster & usually works even if called in non-atomic
> -	 * context.
> +	 * context. get_user_pages_fast does atomic lookup before falling back to
> +	 * slow gup.
>  	 */
>  	rmb();	/* Must/check ms_range_active before loading PTEs */
> -	ret = atomic_pte_lookup(vma, vaddr, write, &paddr, &ps);
> -	if (ret) {
> -		if (atomic)
> +	if (atomic) {
> +		ret = __get_user_pages_fast(vaddr, 1, write, &page);
> +		if (!ret)
>  			goto upm;
> -		if (non_atomic_pte_lookup(vma, vaddr, write, &paddr, &ps))
> +	} else {
> +		ret = get_user_pages_fast(vaddr, 1, write ? FOLL_WRITE : 0, &page);
> +		if (!ret)
>  			goto inval;
>  	}
> +
> +	paddr = page_to_phys(page);
> +	put_user_page(page);
> +
> +	if (unlikely(is_vm_hugetlb_page(vma)))
> +		*pageshift = HPAGE_SHIFT;
> +	else
> +		*pageshift = PAGE_SHIFT;
> +
>  	if (is_gru_paddr(paddr))
>  		goto inval;
> -	paddr = paddr & ~((1UL << ps) - 1);
> +	paddr = paddr & ~((1UL << *pageshift) - 1);
>  	*gpa = uv_soc_phys_ram_to_gpa(paddr);
> -	*pageshift = ps;
> +
>  	return VTOP_SUCCESS;
>  
>  inval:
> -- 
> 2.7.4
>