On 2/14/25 18:16, Sergio Lopez wrote:
> Use the newly introduced SHM_PAGE_SHIFT register to read the page shift
> for the shared memory region, derive the page size from it and store the
> resulting value into virtio_shm_region.
>
> Signed-off-by: Sergio Lopez <slp@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_mmio.c | 11 ++++++++++-
> include/uapi/linux/virtio_mmio.h | 3 +++
> 2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 1f594b626d7a7734e8ec58766737a118c26bad94..0f892770739ea84b3e7be5615332773049b10ab1 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -537,6 +537,7 @@ static bool vm_get_shm_region(struct virtio_device *vdev,
> struct virtio_shm_region *region, u8 id)
> {
> struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> + u8 page_shift = 0;
> u64 len, addr;
>
> /* Select the region we're interested in */
> @@ -560,7 +561,15 @@ static bool vm_get_shm_region(struct virtio_device *vdev,
>
> region->addr = addr;
>
> - region->page_size = 4096;
> + /* If supported by the device transport, read the region page size.
> + * 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))
> + page_shift = (u8) readl(vm_dev->base + VIRTIO_MMIO_SHM_PAGE_SHIFT);
> +
> + region->page_size = 1 << (page_shift + 12);
>
> return true;
> }
> diff --git a/include/uapi/linux/virtio_mmio.h b/include/uapi/linux/virtio_mmio.h
> index 0650f91bea6c70f935764070d825d181a2379afb..43348be30eff90ee228b6490b9d3c35ba4c50aa5 100644
> --- a/include/uapi/linux/virtio_mmio.h
> +++ b/include/uapi/linux/virtio_mmio.h
> @@ -133,6 +133,9 @@
> #define VIRTIO_MMIO_SHM_BASE_LOW 0x0b8
> #define VIRTIO_MMIO_SHM_BASE_HIGH 0x0bc
>
> +/* Shared memory region page shift */
> +#define VIRTIO_MMIO_SHM_PAGE_SHIFT 0x0c4
What's the logic behind choosing 0x0c4, why not 0x0c0?
--
Best regards,
Dmitry
