[PATCH v3 0/1] get_user_pages changes

[PATCH v3 0/1] get_user_pages changes

[Bharath Vedartham]

In this 3rd version of the patch series, I have compressed the patches
of the previous patch series into one patch. This was suggested by Christoph Hellwig.
The suggestion was to remove the pte_lookup functions and use the g
et_user_pages* functions directly instead of the pte_lookup functions.

There is nothing different in this series compared to the previous 
series, It essentially compresses the 3 patches of the original series 
into one patch.

Bharath Vedartham (1):
  sgi-gru: Remove *pte_lookup functions

 drivers/misc/sgi-gru/grufault.c | 114 +++++++++-------------------------------
 1 file changed, 25 insertions(+), 89 deletions(-)

-- 
2.7.4

[PATCH v3 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@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme 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
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 previous patch series.
The review tags were given to the individual patches.
---
 drivers/misc/sgi-gru/grufault.c | 114 +++++++++-------------------------------
 1 file changed, 25 insertions(+), 89 deletions(-)

diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
index 4b713a8..c1258ea 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, &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);
-	*gpa = uv_soc_phys_ram_to_gpa(paddr);
-	*pageshift = ps;
+	paddr = paddr & ~((1UL << *pageshift) - 1);
+	*gpa = uv_soc_phys_ram_to_gpa(paddr);
+
 	return VTOP_SUCCESS;
 
 inval:
-- 
2.7.4

Re: [PATCH v3 1/1] sgi-gru: Remove *pte_lookup functions

[Bharath Vedartham]

On Sat, Jul 27, 2019 at 05:22:28PM +0800, Hillf Danton wrote:
> 
> On Fri, 26 Jul 2019 12:42:26 -0700 (PDT) Bharath Vedartham wrote:
> > 
> >  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, &page);
> > +		if (!ret)
> >  			goto inval;
> >  	}
> > +
> > +	paddr = page_to_phys(page);
> 
> You may drop find_vma() above if PageHuge(page) makes sense here.
I don't think it does. Hugepage support is still incomplete for this
driver.

Thank you
Bharath
> > +	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);
> > -	*gpa = uv_soc_phys_ram_to_gpa(paddr);
> > -	*pageshift = ps;
> > +	paddr = paddr & ~((1UL << *pageshift) - 1);
> > +	*gpa = uv_soc_phys_ram_to_gpa(paddr);
> > +
> >  	return VTOP_SUCCESS;
> >  
> >  inval:
> > -- 
> > 2.7.4
> 

Re: [PATCH v3 1/1] sgi-gru: Remove *pte_lookup functions

[Christoph Hellwig]

On Sat, Jul 27, 2019 at 01:12:00AM +0530, Bharath Vedartham wrote:
> +		ret = get_user_pages_fast(vaddr, 1, write, &page);

I think you want to pass "write ? FOLL_WRITE : 0" here, as
get_user_pages_fast takes a gup_flags argument, not a boolean
write flag.

Re: [PATCH v3 1/1] sgi-gru: Remove *pte_lookup functions

[Bharath Vedartham]

On Mon, Jul 29, 2019 at 08:48:42AM +0200, Christoph Hellwig wrote:
> On Sat, Jul 27, 2019 at 01:12:00AM +0530, Bharath Vedartham wrote:
> > +		ret = get_user_pages_fast(vaddr, 1, write, &page);
> 
> I think you want to pass "write ? FOLL_WRITE : 0" here, as
> get_user_pages_fast takes a gup_flags argument, not a boolean
> write flag.

You are right there! I ll send another version correcting this.

Thank you
Bharath