Re: [PATCH RFC] nvme-ioctl: propagate PRP1 from ioctl to admin cmd

[David Epping <david.epping@missinglinkelectronics.com>]

On Mon, Jun 22, 2026 at 08:35:42AM -0600, Keith Busch wrote:
> On Mon, Jun 22, 2026 at 04:15:42PM +0200, David Epping wrote:
> > @@ -306,6 +306,7 @@ static int nvme_user_cmd(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
> >  	c.common.nsid = cpu_to_le32(cmd.nsid);
> >  	c.common.cdw2[0] = cpu_to_le32(cmd.cdw2);
> >  	c.common.cdw2[1] = cpu_to_le32(cmd.cdw3);
> > +	c.common.dptr.prp1 = cpu_to_le64(cmd.addr);
> 
> This is not correct: the user space virtual address isn't the device
> DMA'able address. The driver already handles mapping the user address to
> kernel space, then to dma, then sets the PRP accordingly.

To clarify, the ioctl struct addr field is not filled with a memory buffer
address by the userspace, but a PCIe mapped BAR address plus offset.
It is obtained by the userspace application operating the FPGA vfio device
by reading from PCI config space via VFIO_PCI_CONFIG_REGION_INDEX.
So it is the address Linux assigned to that BAR (plus offset).