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

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Message-Id: <20190213230455.5605-5-ira.weiny@intel.com>
Date:   Wed, 13 Feb 2019 15:04:52 -0800
From:   ira.weiny@...el.com
To:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, kvm@...r.kernel.org,
        linux-fpga@...r.kernel.org, dri-devel@...ts.freedesktop.org,
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        linux-fbdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        devel@...ts.orangefs.org, linux-mm@...ck.org,
        ceph-devel@...r.kernel.org, rds-devel@....oracle.com
Cc:     Ira Weiny <ira.weiny@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <joro@...tes.org>, Wu Hao <hao.wu@...el.com>,
        Alan Tull <atull@...nel.org>, Moritz Fischer <mdf@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Christian Benvenuti <benve@...co.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matt Porter <mporter@...nel.crashing.org>,
        Alexandre Bounine <alex.bou9@...il.com>,
        Kai Mäkisara <Kai.Makisara@...umbus.fi>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Rob Springer <rspringer@...gle.com>,
        Todd Poynor <toddpoynor@...gle.com>,
        Ben Chan <benchan@...omium.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Martin Brandenburg <martin@...ibond.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH V2 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast

From: Ira Weiny <ira.weiny@...el.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@...el.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