linux-kernel - Re: [PATCH 3/4] block-dma: properly take MMIO path

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Message-ID: <aO1URj3B3IUHX4Ge@kbusch-mbp>
Date: Mon, 13 Oct 2025 13:34:30 -0600
From: Keith Busch <kbusch@...nel.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Jason Gunthorpe <jgg@...dia.com>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH 3/4] block-dma: properly take MMIO path

On Mon, Oct 13, 2025 at 10:29:40PM +0300, Leon Romanovsky wrote:
> On Mon, Oct 13, 2025 at 01:01:18PM -0600, Keith Busch wrote:
> > On Mon, Oct 13, 2025 at 06:34:11PM +0300, Leon Romanovsky wrote:
> > >  static bool blk_dma_map_direct(struct request *req, struct device *dma_dev,
> > >  		struct blk_dma_iter *iter, struct phys_vec *vec)
> > >  {
> > > +	unsigned int attrs = 0;
> > > +
> > > +	if (req->cmd_flags & REQ_MMIO)
> > > +		attrs |= DMA_ATTR_MMIO;
> > 
> > Since data and integrity paylods use these same functions and may point
> > to different kinds of memory, I think you'd have to pass the 'attrs'
> > from the caller since it knows which flags to check for MMIO dma.
> 
> I think that hunk will fix it.
> 
> diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
> index 38f5c34ca223..8af88ba97c7a 100644
> --- a/block/blk-mq-dma.c
> +++ b/block/blk-mq-dma.c
> @@ -88,9 +88,11 @@ static bool blk_dma_map_bus(struct blk_dma_iter *iter, struct phys_vec *vec)
>  static bool blk_dma_map_direct(struct request *req, struct device *dma_dev,
>                 struct blk_dma_iter *iter, struct phys_vec *vec)
>  {
> +       struct bio_integrity_payload *bip = bio_integrity(req->bio);
>         unsigned int attrs = 0;
> 
> -       if (req->cmd_flags & REQ_MMIO)
> +       if ((!bip && req->cmd_flags & REQ_MMIO) ||
> +           bio_integrity_flagged(req->bio, BIP_MMIO))
>                 attrs |= DMA_ATTR_MMIO;

If cmd_flags has REQ_MMIO set, but the integrity flag doesn't have
BIP_MMIO set, you will skip setting DMA_ATTR_MMIO, but I think we need
that set when this is called for the data payload.