On 2/14/25 18:16, Sergio Lopez wrote:
> 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.
>
> Signed-off-by: Sergio Lopez <slp@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_pci_modern.c | 22 +++++++++++++++++-----
> include/uapi/linux/virtio_pci.h | 3 ++-
> 2 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index ab0e1d9148057c431676bfacfe5f68cc97eebb12..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);
> @@ -865,7 +877,7 @@ static bool vp_get_shm_region(struct virtio_device *vdev,
>
> region->len = len;
> region->addr = (u64) phys_addr + offset;
> - region->page_size = 4096;
> + region->page_size = page_size;
>
> return true;
> }
> 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. */
> };
>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
--
Best regards,
Dmitry
