[PATCH for-4.13] nvme-pci: use dma memory for the host memory buffer descriptors

[Christoph Hellwig]

Can I get a quick review for this one?

On Mon, Aug 28, 2017 at 10:47:18AM +0200, Christoph Hellwig wrote:
> The NVMe 1.3 specification says in section 5.21.1.13:
> 
> "After a successful completion of a Set Features enabling the host memory
>  buffer, the host shall not write to the associated host memory region,
>  buffer size, or descriptor list until the host memory buffer has been
>  disabled."
> 
> While this doesn't state that the descriptor list must remain accessible
> to the device it certainly implies it must remaing readable by the device.
> 
> So switch to a dma coherent allocation for the descriptor list just to be
> safe - it's not like the cost for it matters compared to the actual
> memory buffers.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/nvme/host/pci.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 925467b31a33..e5d0a394e49a 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -109,6 +109,7 @@ struct nvme_dev {
>  	/* host memory buffer support: */
>  	u64 host_mem_size;
>  	u32 nr_host_mem_descs;
> +	dma_addr_t host_mem_descs_dma;
>  	struct nvme_host_mem_buf_desc *host_mem_descs;
>  	void **host_mem_desc_bufs;
>  };
> @@ -1565,16 +1566,10 @@ static inline void nvme_release_cmb(struct nvme_dev *dev)
>  
>  static int nvme_set_host_mem(struct nvme_dev *dev, u32 bits)
>  {
> -	size_t len = dev->nr_host_mem_descs * sizeof(*dev->host_mem_descs);
> +	u64 dma_addr = dev->host_mem_descs_dma;
>  	struct nvme_command c;
> -	u64 dma_addr;
>  	int ret;
>  
> -	dma_addr = dma_map_single(dev->dev, dev->host_mem_descs, len,
> -			DMA_TO_DEVICE);
> -	if (dma_mapping_error(dev->dev, dma_addr))
> -		return -ENOMEM;
> -
>  	memset(&c, 0, sizeof(c));
>  	c.features.opcode	= nvme_admin_set_features;
>  	c.features.fid		= cpu_to_le32(NVME_FEAT_HOST_MEM_BUF);
> @@ -1591,7 +1586,6 @@ static int nvme_set_host_mem(struct nvme_dev *dev, u32 bits)
>  			 "failed to set host mem (err %d, flags %#x).\n",
>  			 ret, bits);
>  	}
> -	dma_unmap_single(dev->dev, dma_addr, len, DMA_TO_DEVICE);
>  	return ret;
>  }
>  
> @@ -1609,7 +1603,9 @@ static void nvme_free_host_mem(struct nvme_dev *dev)
>  
>  	kfree(dev->host_mem_desc_bufs);
>  	dev->host_mem_desc_bufs = NULL;
> -	kfree(dev->host_mem_descs);
> +	dma_free_coherent(dev->dev,
> +			dev->nr_host_mem_descs * sizeof(*dev->host_mem_descs),
> +			dev->host_mem_descs, dev->host_mem_descs_dma);
>  	dev->host_mem_descs = NULL;
>  }
>  
> @@ -1617,6 +1613,7 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>  {
>  	struct nvme_host_mem_buf_desc *descs;
>  	u32 chunk_size, max_entries, len;
> +	dma_addr_t descs_dma;
>  	int i = 0;
>  	void **bufs;
>  	u64 size = 0, tmp;
> @@ -1627,7 +1624,8 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>  	tmp = (preferred + chunk_size - 1);
>  	do_div(tmp, chunk_size);
>  	max_entries = tmp;
> -	descs = kcalloc(max_entries, sizeof(*descs), GFP_KERNEL);
> +	descs = dma_zalloc_coherent(dev->dev, max_entries * sizeof(*descs),
> +			&descs_dma, GFP_KERNEL);
>  	if (!descs)
>  		goto out;
>  
> @@ -1661,6 +1659,7 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>  	dev->nr_host_mem_descs = i;
>  	dev->host_mem_size = size;
>  	dev->host_mem_descs = descs;
> +	dev->host_mem_descs_dma = descs_dma;
>  	dev->host_mem_desc_bufs = bufs;
>  	return 0;
>  
> @@ -1674,7 +1673,8 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>  
>  	kfree(bufs);
>  out_free_descs:
> -	kfree(descs);
> +	dma_free_coherent(dev->dev, max_entries * sizeof(*dev->host_mem_descs),
> +			descs, descs_dma);
>  out:
>  	/* try a smaller chunk size if we failed early */
>  	if (chunk_size >= PAGE_SIZE * 2 && (i == 0 || size < min)) {
> -- 
> 2.11.0
> 
> 
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