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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Parav Pandit <parav@nvidia.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.14 14/23] virtio: Improve vq->broken access to avoid any compiler optimization
Date: Wed,  1 Sep 2021 14:26:59 +0200	[thread overview]
Message-ID: <20210901122250.250207188@linuxfoundation.org> (raw)
In-Reply-To: <20210901122249.786673285@linuxfoundation.org>

From: Parav Pandit <parav@nvidia.com>

[ Upstream commit 60f0779862e4ab943810187752c462e85f5fa371 ]

Currently vq->broken field is read by virtqueue_is_broken() in busy
loop in one context by virtnet_send_command().

vq->broken is set to true in other process context by
virtio_break_device(). Reader and writer are accessing it without any
synchronization. This may lead to a compiler optimization which may
result to optimize reading vq->broken only once.

Hence, force reading vq->broken on each invocation of
virtqueue_is_broken() and also force writing it so that such
update is visible to the readers.

It is a theoretical fix that isn't yet encountered in the field.

Signed-off-by: Parav Pandit <parav@nvidia.com>
Link: https://lore.kernel.org/r/20210721142648.1525924-2-parav@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/virtio/virtio_ring.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 51278f8bd3ab..22a4329ed200 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1198,7 +1198,7 @@ bool virtqueue_is_broken(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	return vq->broken;
+	return READ_ONCE(vq->broken);
 }
 EXPORT_SYMBOL_GPL(virtqueue_is_broken);
 
@@ -1212,7 +1212,9 @@ void virtio_break_device(struct virtio_device *dev)
 
 	list_for_each_entry(_vq, &dev->vqs, list) {
 		struct vring_virtqueue *vq = to_vvq(_vq);
-		vq->broken = true;
+
+		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
+		WRITE_ONCE(vq->broken, true);
 	}
 }
 EXPORT_SYMBOL_GPL(virtio_break_device);
-- 
2.30.2




  parent reply	other threads:[~2021-09-01 12:29 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01 12:26 [PATCH 4.14 00/23] 4.14.246-rc1 review Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 01/23] ARC: Fix CONFIG_STACKDEPOT Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 02/23] can: usb: esd_usb2: esd_usb2_rx_event(): fix the interchange of the CAN RX and TX error counters Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 03/23] Revert "USB: serial: ch341: fix character loss at high transfer rates" Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 04/23] USB: serial: option: add new VID/PID to support Fibocom FG150 Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 05/23] usb: dwc3: gadget: Fix dwc3_calc_trbs_left() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 06/23] usb: dwc3: gadget: Stop EP0 transfers during pullup disable Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 07/23] IB/hfi1: Fix possible null-pointer dereference in _extend_sdma_tx_descs() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 08/23] e1000e: Fix the max snoop/no-snoop latency for 10M Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 09/23] ip_gre: add validation for csum_start Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 10/23] xgene-v2: Fix a resource leak in the error handling path of xge_probe() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 11/23] net: marvell: fix MVNETA_TX_IN_PRGRS bit number Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 12/23] usb: gadget: u_audio: fix race condition on endpoint stop Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 13/23] opp: remove WARN when no valid OPPs remain Greg Kroah-Hartman
2021-09-01 12:26 ` Greg Kroah-Hartman [this message]
2021-09-01 12:27 ` [PATCH 4.14 15/23] vringh: Use wiov->used to check for read/write desc order Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 16/23] drm: Copy drm_wait_vblank to user before returning Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 17/23] drm/nouveau/disp: power down unused DP links during init Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 18/23] net/rds: dma_map_sg is entitled to merge entries Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 19/23] vt_kdsetmode: extend console locking Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 20/23] fbmem: add margin check to fb_check_caps() Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 21/23] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP shadow MMUs Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 22/23] KVM: X86: MMU: Use the correct inherited permissions to get shadow page Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 23/23] Revert "floppy: reintroduce O_NDELAY fix" Greg Kroah-Hartman
2021-09-01 19:21 ` [PATCH 4.14 00/23] 4.14.246-rc1 review Jon Hunter
2021-09-01 19:22 ` Jon Hunter
2021-09-02  1:08 ` Samuel Zou
2021-09-02 16:08 ` Naresh Kamboju
2021-09-02 21:50 ` Guenter Roeck

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