linux-kernel - [PATCH 3/4] mm/hmm: allow hmm_range_fault() of mmap(PROT

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Message-ID: <20190911222829.28874-4-rcampbell@nvidia.com>
Date:   Wed, 11 Sep 2019 15:28:28 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     <linux-mm@...ck.org>
CC:     <linux-kernel@...r.kernel.org>, <amd-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <nouveau@...ts.freedesktop.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Christoph Hellwig" <hch@....de>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: [PATCH 3/4] mm/hmm: allow hmm_range_fault() of mmap(PROT_NONE)

Allow hmm_range_fault() to return success (0) when the range has no access
(!(vma->vm_flags & VM_READ)). The range->pfns[] array will be filled with
range->values[HMM_PFN_NONE] in this case.
This allows the caller to get a snapshot of a range without having to
lookup the vma before calling hmm_range_fault().
If the call to hmm_range_fault() is not a snapshot, the caller can still
check that pfns have the desired access permissions.

Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
Cc: "Jérôme Glisse" <jglisse@...hat.com>
Cc: Jason Gunthorpe <jgg@...lanox.com>
Cc: Christoph Hellwig <hch@....de>
---
 mm/hmm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 7217912bef13..16c834e5d1c0 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -795,7 +795,9 @@ static int hmm_vma_walk_test(unsigned long start,
 	 */
 	if (!(vma->vm_flags & VM_READ)) {
 		(void) hmm_pfns_fill(start, end, range, HMM_PFN_NONE);
-		return -EPERM;
+
+		/* Skip this vma and continue processing the next vma. */
+		return 1;
 	}
 
 	return 0;
-- 
2.20.1