linux-kernel - [PATCH 4.19 60/93] drm/ttm: Restore ttm prefaulting

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Message-Id: <20191027203304.610117369@linuxfoundation.org>
Date:   Sun, 27 Oct 2019 22:01:12 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Souptick Joarder <jrdr.linux@...il.com>,
        Christian König <christian.koenig@....com>,
        Thomas Hellstrom <thellstrom@...are.com>
Subject: [PATCH 4.19 60/93] drm/ttm: Restore ttm prefaulting

From: Thomas Hellstrom <thellstrom@...are.com>

commit 941f2f72dbbe0cf8c2d6e0b180a8021a0ec477fa upstream.

Commit 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
broke TTM prefaulting. Since vmf_insert_mixed() typically always returns
VM_FAULT_NOPAGE, prefaulting stops after the second PTE.

Restore (almost) the original behaviour. Unfortunately we can no longer
with the new vm_fault_t return type determine whether a prefaulting
PTE insertion hit an already populated PTE, and terminate the insertion
loop. Instead we continue with the pre-determined number of prefaults.

Fixes: 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
Cc: Souptick Joarder <jrdr.linux@...il.com>
Cc: Christian König <christian.koenig@....com>
Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
Reviewed-by: Christian König <christian.koenig@....com>
Cc: stable@...r.kernel.org # v4.19+
Signed-off-by: Christian König <christian.koenig@....com>
Link: https://patchwork.freedesktop.org/patch/330387/
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/ttm/ttm_bo_vm.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -273,15 +273,13 @@ static vm_fault_t ttm_bo_vm_fault(struct
 		else
 			ret = vmf_insert_pfn(&cvma, address, pfn);
 
-		/*
-		 * Somebody beat us to this PTE or prefaulting to
-		 * an already populated PTE, or prefaulting error.
-		 */
-
-		if (unlikely((ret == VM_FAULT_NOPAGE && i > 0)))
-			break;
-		else if (unlikely(ret & VM_FAULT_ERROR))
-			goto out_io_unlock;
+		/* Never error on prefaulted PTEs */
+		if (unlikely((ret & VM_FAULT_ERROR))) {
+			if (i == 0)
+				goto out_io_unlock;
+			else
+				break;
+		}
 
 		address += PAGE_SIZE;
 		if (unlikely(++page_offset >= page_last))