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Message-Id: <20250220-virtio-shm-page-size-v3-2-874fff6f3979@redhat.com>
Date: Thu, 20 Feb 2025 15:28:51 +0100
From: Sergio Lopez <slp@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>,
Daniel Verkamp <dverkamp@...omium.org>, 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 v3 2/4] virtio-pci: extend virtio_pci_cap with
page_shift
If VIRTIO_F_SHM_PAGE_SIZE has been negotiated and cfg_type is
VIRTIO_PCI_CAP_SHARED_MEMORY_CFG, the driver must read the page_shift
field, derive the supported page size from it, and honor it when
requesting the map of memory into the shared memory region to the
device.
Extend virtio_pci_cap to hold that field, and use it to feed
virtio_shm_region with the corresponding page size.
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
Signed-off-by: Sergio Lopez <slp@...hat.com>
---
drivers/virtio/virtio_mmio.c | 2 ++
drivers/virtio/virtio_pci_modern.c | 21 +++++++++++++++++----
include/linux/virtio_config.h | 1 +
include/uapi/linux/virtio_pci.h | 3 ++-
4 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 5d78c2d572abfcfe2b84cdd82df622320fe97d5d..1f594b626d7a7734e8ec58766737a118c26bad94 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;
+
return true;
}
diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 104ba08f82d4a6268240bbad15385dd44b3a71d6..562a8e1c2bfe6876cffabe26f02cd61ad7fea2cd 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -770,14 +770,15 @@ static void del_vq(struct virtio_pci_vq_info *info)
vring_del_virtqueue(vq);
}
-static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
- u8 *bar, u64 *offset, u64 *len)
+static int virtio_pci_find_shm_cap(struct virtio_device *vdev, struct pci_dev *dev,
+ u8 required_id, u8 *bar, u64 *offset, u64 *len,
+ u32 *page_size)
{
int pos;
for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR); pos > 0;
pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
- u8 type, cap_len, id, res_bar;
+ u8 type, cap_len, id, res_bar, page_shift = 0;
u32 tmp32;
u64 res_offset, res_length;
@@ -808,6 +809,15 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
* Looks good.
*/
+ /* Read the page shift if supported. The page_shift variable is
+ * initialized to zero above, so if this feature isn't supported it
+ * will result in a page_size of 4096, a default safe value.
+ */
+ if (__virtio_test_bit(vdev, VIRTIO_F_SHM_PAGE_SIZE)) {
+ pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap,
+ page_shift), &page_shift);
+ }
+
/* Read the lower 32bit of length and offset */
pci_read_config_dword(dev, pos + offsetof(struct virtio_pci_cap,
offset), &tmp32);
@@ -829,6 +839,7 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
*bar = res_bar;
*offset = res_offset;
*len = res_length;
+ *page_size = 1 << (page_shift + 12);
return pos;
}
@@ -841,11 +852,12 @@ static bool vp_get_shm_region(struct virtio_device *vdev,
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
struct pci_dev *pci_dev = vp_dev->pci_dev;
u8 bar;
+ u32 page_size;
u64 offset, len;
phys_addr_t phys_addr;
size_t bar_len;
- if (!virtio_pci_find_shm_cap(pci_dev, id, &bar, &offset, &len))
+ if (!virtio_pci_find_shm_cap(vdev, pci_dev, id, &bar, &offset, &len, &page_size))
return false;
phys_addr = pci_resource_start(pci_dev, bar);
@@ -865,6 +877,7 @@ static bool vp_get_shm_region(struct virtio_device *vdev,
region->len = len;
region->addr = (u64) phys_addr + offset;
+ region->page_size = page_size;
return true;
}
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 169c7d367facb36dcabf9596068580ea8b8516c7..c1b2ce71ea55e81978e18db05494deab193fa4fb 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;
+ u32 page_size;
};
typedef void vq_callback_t(struct virtqueue *);
diff --git a/include/uapi/linux/virtio_pci.h b/include/uapi/linux/virtio_pci.h
index 8549d4571257142ac6c9dad5c01369923791a85a..1a76df52b4eccf548df78a8ee7d3a04591f55522 100644
--- a/include/uapi/linux/virtio_pci.h
+++ b/include/uapi/linux/virtio_pci.h
@@ -127,7 +127,8 @@ struct virtio_pci_cap {
__u8 cfg_type; /* Identifies the structure. */
__u8 bar; /* Where to find it. */
__u8 id; /* Multiple capabilities of the same type */
- __u8 padding[2]; /* Pad to full dword. */
+ __u8 page_shift; /* Page shift for VIRTIO_PCI_CAP_SHARED_MEMORY_CFG. */
+ __u8 padding[1]; /* Pad to full dword. */
__le32 offset; /* Offset within bar. */
__le32 length; /* Length of the structure, in bytes. */
};
--
2.48.1
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