[PATCH v2 1/1] virtio: blk: support block sizes exceeding 512 bytes

[Andre Przywara]

On Sat, 30 Aug 2025 22:39:54 +0200
Heinrich Schuchardt <heinrich.schuchardt at canonical.com> wrote:

Hi Heinrich,

> QEMU allows to specify the logical block size via parameter
> logical_block_size of a virtio-blk-device.
> 
> The communication channel via virtqueues remains based on 512 byte blocks
> even if the logical_block_size is larger.
> 
> Consider the logical block size in the block device driver.
> 
> Reported-by: Emil Renner Berthing <emil.renner.berthing at canonical.com>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
> v2:
> 	remove superfluous include linux/err.h
> ---
>  drivers/virtio/virtio_blk.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> index 2f999fc8bbe..4224e3c17f4 100644
> --- a/drivers/virtio/virtio_blk.c
> +++ b/drivers/virtio/virtio_blk.c
> @@ -12,10 +12,17 @@
>  #include <virtio_types.h>
>  #include <virtio.h>
>  #include <virtio_ring.h>
> +#include <linux/log2.h>
>  #include "virtio_blk.h"
>  
> +/**
> + * struct virtio_blk_priv - private date for virtio block device
> + */
>  struct virtio_blk_priv {
> +	/** @virtqueue - virtqueue to process */
>  	struct virtqueue *vq;
> +	/** @blksz_shift - log2 of block size divided by 512 */
> +	u32 blksz_shift;
>  };
>  
>  static const u32 feature[] = {
> @@ -71,6 +78,8 @@ static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
>  	u8 status;
>  	int ret;
>  
> +	sector <<= priv->blksz_shift;
> +	blkcnt <<= priv->blksz_shift;
>  	virtio_blk_init_header_sg(dev, sector, type, &out_hdr, &hdr_sg);
>  	sgs[num_out++] = &hdr_sg;
>  
> @@ -109,7 +118,7 @@ static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
>  		;
>  	log_debug("done\n");
>  
> -	return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;
> +	return status == VIRTIO_BLK_S_OK ? blkcnt >> priv->blksz_shift : -EIO;
>  }
>  
>  static ulong virtio_blk_read(struct udevice *dev, lbaint_t start,
> @@ -177,15 +186,25 @@ static int virtio_blk_probe(struct udevice *dev)
>  	struct blk_desc *desc = dev_get_uclass_plat(dev);
>  	u64 cap;
>  	int ret;
> +	u32 blk_size;
>  
>  	ret = virtio_find_vqs(dev, 1, &priv->vq);
>  	if (ret)
>  		return ret;
>  
> -	desc->blksz = 512;
> -	desc->log2blksz = 9;
>  	virtio_cread(dev, struct virtio_blk_config, capacity, &cap);
>  	desc->lba = cap;
> +	if (!virtio_has_feature(dev, VIRTIO_BLK_F_BLK_SIZE)) {

Is that actually the right condition check? I would assume that we only
query the blk_size field if the feature bit is *set*, not when it's
cleared?
We see a failure (virtio block device not registering), because blk_size is
0 on the Arm FVP fast model, which is fine I think because the feature bit
is clear as well.

Cheers,
Andre

> +		virtio_cread(dev, struct virtio_blk_config, blk_size, &blk_size);
> +		desc->blksz = blk_size;
> +		if (!is_power_of_2(blk_size) || desc->blksz < 512)
> +			return -EIO;
> +	} else {
> +		desc->blksz = 512;
> +	}
> +	desc->log2blksz = LOG2(desc->blksz);
> +	priv->blksz_shift = desc->log2blksz - 9;
> +	desc->lba >>= priv->blksz_shift;
>  
>  	return 0;
>  }