linux-kernel - [PATCH 12/15] HMM: fork copy migrated memory into system memory for child process.

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Date:	Thu, 13 Aug 2015 15:37:28 -0400
From:	Jérôme Glisse <jglisse@...hat.com>
To:	akpm@...ux-foundation.org, <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, <joro@...tes.org>,
	Mel Gorman <mgorman@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <jweiner@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Airlie <airlied@...hat.com>,
	Brendan Conoboy <blc@...hat.com>,
	Joe Donohue <jdonohue@...hat.com>,
	Christophe Harle <charle@...dia.com>,
	Duncan Poole <dpoole@...dia.com>,
	Sherry Cheung <SCheung@...dia.com>,
	Subhash Gutti <sgutti@...dia.com>,
	John Hubbard <jhubbard@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Lucien Dunning <ldunning@...dia.com>,
	Cameron Buschardt <cabuschardt@...dia.com>,
	Arvind Gopalakrishnan <arvindg@...dia.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Liran Liss <liranl@...lanox.com>,
	Roland Dreier <roland@...estorage.com>,
	Ben Sander <ben.sander@....com>,
	Greg Stoner <Greg.Stoner@....com>,
	John Bridgman <John.Bridgman@....com>,
	Michael Mantor <Michael.Mantor@....com>,
	Paul Blinzer <Paul.Blinzer@....com>,
	Leonid Shamis <Leonid.Shamis@....com>,
	Laurent Morichetti <Laurent.Morichetti@....com>,
	Alexander Deucher <Alexander.Deucher@....com>,
	Jérôme Glisse <jglisse@...hat.com>
Subject: [PATCH 12/15] HMM: fork copy migrated memory into system memory for child process.

When forking if process being fork had any memory migrated to some
device memory, we need to make a system copy for the child process.
Latter patches can revisit this and use the same COW semantic for
device memory.

Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
---
 mm/hmm.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 5400dfb..e23b264 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -480,7 +480,37 @@ int hmm_mm_fork(struct mm_struct *src_mm,
 		unsigned long start,
 		unsigned long end)
 {
-	return -ENOMEM;
+	unsigned long npages = (end - start) >> PAGE_SHIFT;
+	struct hmm_event event;
+	dma_addr_t *dst;
+	struct hmm *hmm;
+	pte_t *new_pte;
+	int ret;
+
+	hmm = hmm_ref(src_mm->hmm);
+	if (!hmm)
+		return -EINVAL;
+
+
+	dst = kcalloc(npages, sizeof(*dst), GFP_KERNEL);
+	if (!dst) {
+		hmm_unref(hmm);
+		return -ENOMEM;
+	}
+	new_pte = kcalloc(npages, sizeof(*new_pte), GFP_KERNEL);
+	if (!new_pte) {
+		kfree(dst);
+		hmm_unref(hmm);
+		return -ENOMEM;
+	}
+
+	hmm_event_init(&event, hmm, start, end, HMM_FORK);
+	ret = hmm_migrate_back(hmm, &event, dst_mm, dst_vma, new_pte,
+			       dst, start, end);
+	hmm_unref(hmm);
+	kfree(new_pte);
+	kfree(dst);
+	return ret;
 }
 EXPORT_SYMBOL(hmm_mm_fork);
 
@@ -656,6 +686,12 @@ static void hmm_mirror_update_pte(struct hmm_mirror *mirror,
 	}
 
 	if (hmm_pte_test_valid_dev(hmm_pte)) {
+		/*
+		 * On fork device memory is duplicated so no need to write
+		 * protect it.
+		 */
+		if (event->etype == HMM_FORK)
+			return;
 		*hmm_pte &= event->pte_mask;
 		if (!hmm_pte_test_valid_dev(hmm_pte))
 			hmm_pt_iter_directory_unref(iter);
-- 
1.9.3

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