[PATCH] mm/hmm: hmm_range_fault handle pages swapped out

From: "Yang, Philip" <Philip.Yang@amd.com>
To: "jglisse@redhat.com" <jglisse@redhat.com>,
	"alex.deucher@amd.com" <alex.deucher@amd.com>,
	"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
	"Kuehling, Felix" <Felix.Kuehling@amd.com>,
	"jgg@mellanox.com" <jgg@mellanox.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Cc: "Yang, Philip" <Philip.Yang@amd.com>
Subject: [PATCH] mm/hmm: hmm_range_fault handle pages swapped out
Date: Thu, 15 Aug 2019 20:52:56 +0000	[thread overview]
Message-ID: <20190815205227.7949-1-Philip.Yang@amd.com> (raw)

hmm_range_fault may return NULL pages because some of pfns are equal to
HMM_PFN_NONE. This happens randomly under memory pressure. The reason is
for swapped out page pte path, hmm_vma_handle_pte doesn't update fault
variable from cpu_flags, so it failed to call hmm_vam_do_fault to swap
the page in.

The fix is to call hmm_pte_need_fault to update fault variable.

Change-Id: I2e8611485563d11d938881c18b7935fa1e7c91ee
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
---
 mm/hmm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hmm.c b/mm/hmm.c
index 9f22562e2c43..7ca4fb39d3d8 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -544,6 +544,9 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 		swp_entry_t entry = pte_to_swp_entry(pte);
 
 		if (!non_swap_entry(entry)) {
+			cpu_flags = pte_to_hmm_pfn_flags(range, pte);
+			hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
+					   &fault, &write_fault);
 			if (fault || write_fault)
 				goto fault;
 			return 0;
-- 
2.17.1


