linux-kernel - [PATCH RFC 2/5] virtio: introduce VIRTIO_F_SHM_PAGE

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Message-Id: <20250213-virtio-shm-page-size-v1-2-5ee1f9984350@redhat.com>
Date: Thu, 13 Feb 2025 16:49:16 +0100
From: Sergio Lopez <slp@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
 Eugenio Pérez <eperezma@...hat.com>, 
 David Airlie <airlied@...hat.com>, Gerd Hoffmann <kraxel@...hat.com>, 
 Gurchetan Singh <gurchetansingh@...omium.org>, 
 Chia-I Wu <olvaffe@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 Simona Vetter <simona@...ll.ch>, Rob Clark <robdclark@...il.com>, 
 Dmitry Osipenko <dmitry.osipenko@...labora.com>, fnkl.kernel@...il.com
Cc: virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, Sergio Lopez <slp@...hat.com>
Subject: [PATCH RFC 2/5] virtio: introduce VIRTIO_F_SHM_PAGE_SIZE

Introduce VIRTIO_F_SHM_PAGE_SIZE, a feature bit which indicates that the
transport provides the page size for SHM regions.

Signed-off-by: Sergio Lopez <slp@...hat.com>
---
 drivers/virtio/virtio_pci_modern.c | 3 +++
 drivers/virtio/virtio_ring.c       | 2 ++
 include/uapi/linux/virtio_config.h | 7 ++++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 4e6c28aacd1b5dfc117337a689a25d668805e334..79616ce5057bf3b2b88cae7e8fb7729efa9dd632 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -367,6 +367,9 @@ static void vp_transport_features(struct virtio_device *vdev, u64 features)

 	if (features & BIT_ULL(VIRTIO_F_ADMIN_VQ))
 		__virtio_set_bit(vdev, VIRTIO_F_ADMIN_VQ);
+
+	if (features & BIT_ULL(VIRTIO_F_SHM_PAGE_SIZE))
+		__virtio_set_bit(vdev, VIRTIO_F_SHM_PAGE_SIZE);
 }

 static int __vp_check_common_size_one_feature(struct virtio_device *vdev, u32 fbit,
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fdd2d2b07b5a2aca864bc917306536685afb66a6..d853d5cf7e553be8bbe0ff461dc7312b258c6e58 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2983,6 +2983,8 @@ void vring_transport_features(struct virtio_device *vdev)
 			break;
 		case VIRTIO_F_NOTIFICATION_DATA:
 			break;
+		case VIRTIO_F_SHM_PAGE_SIZE:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);
diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
index 2445f365bce74b4e926c6929322b269252ab6830..3171e3792263c2cd472ac09da18e593ab400751d 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -52,7 +52,7 @@
  * rest are per-device feature bits.
  */
 #define VIRTIO_TRANSPORT_F_START	28
-#define VIRTIO_TRANSPORT_F_END		42
+#define VIRTIO_TRANSPORT_F_END		43

 #ifndef VIRTIO_CONFIG_NO_LEGACY
 /* Do we get callbacks when the ring is completely used, even if we've
@@ -120,4 +120,9 @@
  */
 #define VIRTIO_F_ADMIN_VQ		41

+/*
+ * This feature indicates that the transport provides the SHM page size.
+ */
+#define VIRTIO_F_SHM_PAGE_SIZE		42
+
 #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */

-- 
2.48.1