[PATCH V2 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast

From: ira.weiny@intel.com
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Cc: "Ira Weiny" <ira.weiny@intel.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Cornelia Huck" <cohuck@redhat.com>,
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	"Daniel Vetter" <daniel@ffwll.ch>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Dennis Dalessandro" <dennis.dalessandro@intel.com>,
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	"Kai Mäkisara" <Kai.Makisara@kolumbus.fi>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	"Rob Springer" <rspringer@google.com>,
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	"Bartlomiej Zolnierkiewicz" <b.zolnierkie@samsung.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Martin Brandenburg" <martin@omnibond.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Michal Hocko" <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH V2 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast
Date: Wed, 13 Feb 2019 15:04:52 -0800	[thread overview]
Message-ID: <20190213230455.5605-5-ira.weiny@intel.com> (raw)
In-Reply-To: <20190213230455.5605-1-ira.weiny@intel.com>

From: Ira Weiny <ira.weiny@intel.com>

DAX pages were previously unprotected from longterm pins when users
called get_user_pages_fast().

Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall
back to regular GUP processing if a DEVMAP page is encountered.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
 mm/gup.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 6f32d36b3c5b..f7e759c523bb 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1439,6 +1439,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 			goto pte_unmap;
 
 		if (pte_devmap(pte)) {
+			if (unlikely(flags & FOLL_LONGTERM))
+				goto pte_unmap;
+
 			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
 			if (unlikely(!pgmap)) {
 				undo_dev_pagemap(nr, nr_start, pages);
@@ -1578,8 +1581,11 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
 		return 0;
 
-	if (pmd_devmap(orig))
+	if (pmd_devmap(orig)) {
+		if (unlikely(flags & FOLL_LONGTERM))
+			return 0;
 		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
+	}
 
 	refs = 0;
 	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
@@ -1904,8 +1910,20 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 		start += nr << PAGE_SHIFT;
 		pages += nr;
 
-		ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
-					      gup_flags);
+		if (gup_flags & FOLL_LONGTERM) {
+			down_read(&current->mm->mmap_sem);
+			ret = __gup_longterm_locked(current, current->mm,
+						    start, nr_pages - nr,
+						    pages, NULL, gup_flags);
+			up_read(&current->mm->mmap_sem);
+		} else {
+			/*
+			 * retain FAULT_FOLL_ALLOW_RETRY optimization if
+			 * possible
+			 */
+			ret = get_user_pages_unlocked(start, nr_pages - nr,
+						      pages, gup_flags);
+		}
 
 		/* Have to be a bit careful with return values */
 		if (nr > 0) {
-- 
2.20.1

