linux-kernel - [PATCH RFC 1/5] virtio_config: add page_size field to virtio_shm

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Message-Id: <20250213-virtio-shm-page-size-v1-1-5ee1f9984350@redhat.com>
Date: Thu, 13 Feb 2025 16:49:15 +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 1/5] virtio_config: add page_size field to
 virtio_shm_region

Add a page_size field to virtio_shm_region to store page size supported
by the device. This is required to support running VMs with a page size
smaller than the host, among other potential scenarios.

Signed-off-by: Sergio Lopez <slp@...hat.com>
---
 drivers/virtio/virtio_mmio.c       | 2 ++
 drivers/virtio/virtio_pci_modern.c | 1 +
 include/linux/virtio_config.h      | 1 +
 3 files changed, 4 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 5d78c2d572abfcfe2b84cdd82df622320fe97d5d..cd0a0407659517e6a318b117ba67258c59f1f983 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -560,6 +560,8 @@ static bool vm_get_shm_region(struct virtio_device *vdev,

 	region->addr = addr;

+	region->page_size = 4096 >> 12;
+
 	return true;
 }

diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 5eaade7578606e4b02af0d66447417ad6aa11064..4e6c28aacd1b5dfc117337a689a25d668805e334 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -862,6 +862,7 @@ static bool vp_get_shm_region(struct virtio_device *vdev,

 	region->len = len;
 	region->addr = (u64) phys_addr + offset;
+	region->page_size = 4096 >> 12;

 	return true;
 }
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 169c7d367facb36dcabf9596068580ea8b8516c7..21ada8fcdf655894bb725045f54c9db3a1492b13 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -14,6 +14,7 @@ struct irq_affinity;
 struct virtio_shm_region {
 	u64 addr;
 	u64 len;
+	u16 page_size; /* PAGE_SIZE >> 12 */
 };

 typedef void vq_callback_t(struct virtqueue *);

-- 
2.48.1