[Linux-kernel-mentees][PATCH v4 1/1] sgi-gru: Remove *pte_lookup functions

[Bharath Vedartham]

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 which does not fall back to slow
get_user_pages. get_user_pages_fast on the other hand tries to use
__get_user_pages_fast but fallbacks to slow get_user_pages if
__get_user_pages_fast fails.

Also unnecessary ifdefs to check for CONFIG_HUGETLB is removed as the
check is redundant.

Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Dimitri Sivanich <sivanich@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel-mentees@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Signed-off-by: Bharath Vedartham <linux.bhar@xxxxxxxxx>
---
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.
---
 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