linux-kernel - Re: [PATCH v3 2/2] block-dma: properly take MMIO path

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Message-ID: <aRSbzwpS2AuP92_n@kbusch-mbp>
Date: Wed, 12 Nov 2025 09:38:07 -0500
From: Keith Busch <kbusch@...nel.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v3 2/2] block-dma: properly take MMIO path

On Mon, Oct 27, 2025 at 09:30:21AM +0200, Leon Romanovsky wrote:
> @@ -732,13 +746,20 @@ static void nvme_unmap_metadata(struct request *req)
>  		return;
>  	}
>  
> -	if (!blk_rq_integrity_dma_unmap(req, dma_dev, &iod->meta_dma_state,
> -					iod->meta_total_len)) {
> +	if (iod->flags & IOD_META_P2P)
> +		map = PCI_P2PDMA_MAP_BUS_ADDR;
> +	if (iod->flags & IOD_META_MMIO) {
> +		map = PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
> +		attrs |= DMA_ATTR_MMIO;
> +	}

This should be an 'else if' no?

> @@ -760,12 +783,20 @@ static void nvme_unmap_data(struct request *req)
>  		return;
>  	}
>  
> -	if (!blk_rq_dma_unmap(req, dma_dev, &iod->dma_state, iod->total_len)) {
> +	if (iod->flags & IOD_DATA_P2P)
> +		map = PCI_P2PDMA_MAP_BUS_ADDR;
> +	if (iod->flags & IOD_DATA_MMIO) {
> +		map = PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
> +		attrs |= DMA_ATTR_MMIO;
> +	}

Same here.

> @@ -1036,6 +1067,17 @@ static blk_status_t nvme_map_data(struct request *req)
>  	if (!blk_rq_dma_map_iter_start(req, dev->dev, &iod->dma_state, &iter))
>  		return iter.status;
>  
> +	switch (iter.p2pdma.map) {
> +	case PCI_P2PDMA_MAP_BUS_ADDR:
> +		iod->flags |= IOD_DATA_P2P;
> +		break;
> +	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +		iod->flags |= IOD_DATA_MMIO;
> +		break;
> +	default:
> +		return BLK_STS_RESOURCE;
> +	}

Why is it an error if the data isn't a P2PDMA type?

> @@ -1058,6 +1100,17 @@ static blk_status_t nvme_pci_setup_meta_sgls(struct request *req)
>  						&iod->meta_dma_state, &iter))
>  		return iter.status;
>  
> +	switch (iter.p2pdma.map) {
> +	case PCI_P2PDMA_MAP_BUS_ADDR:
> +		iod->flags |= IOD_META_P2P;
> +		break;
> +	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +		iod->flags |= IOD_META_MMIO;
> +		break;
> +	default:
> +		return BLK_STS_RESOURCE;
> +	}

Same here.