Re: [PATCH 2/3] vfio/pci: refactor vfio_pci_bar_rw

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 12 Dec 2024 15:50:49 -0500
Yunxiang Li <Yunxiang.Li@amd.com> wrote:

> In the next patch the logic for reading ROM will get more complicated,
> so decouple the ROM path from the normal path. Also check that for ROM
> write is not allowed.

This is already enforced by the caller.  Vague references to the next
patch don't make a lot of sense once commits are in the tree, this
should describe what you're preparing for.

> 
> Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
> ---
>  drivers/vfio/pci/vfio_pci_rdwr.c | 47 ++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index a1eeacad82120..4bed9fd5af50f 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -236,10 +236,9 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_core_device *vdev, char __user *buf,
>  	struct pci_dev *pdev = vdev->pdev;
>  	loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
>  	int bar = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> -	size_t x_start = 0, x_end = 0;
> +	size_t x_start, x_end;
>  	resource_size_t end;
>  	void __iomem *io;
> -	struct resource *res = &vdev->pdev->resource[bar];
>  	ssize_t done;
>  
>  	if (pci_resource_start(pdev, bar))
> @@ -253,41 +252,43 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_core_device *vdev, char __user *buf,
>  	count = min(count, (size_t)(end - pos));
>  
>  	if (bar == PCI_ROM_RESOURCE) {
> +		if (iswrite)
> +			return -EINVAL;
>  		/*
>  		 * The ROM can fill less space than the BAR, so we start the
>  		 * excluded range at the end of the actual ROM.  This makes
>  		 * filling large ROM BARs much faster.
>  		 */
>  		io = pci_map_rom(pdev, &x_start);
> -		if (!io) {
> -			done = -ENOMEM;
> -			goto out;
> -		}
> +		if (!io)
> +			return -ENOMEM;
>  		x_end = end;
> +
> +		done = vfio_pci_core_do_io_rw(vdev, 1, io, buf, pos,
> +					      count, x_start, x_end, 0);
> +
> +		pci_unmap_rom(pdev, io);
>  	} else {
> -		int ret = vfio_pci_core_setup_barmap(vdev, bar);
> -		if (ret) {
> -			done = ret;
> -			goto out;
> -		}
> +		done = vfio_pci_core_setup_barmap(vdev, bar);
> +		if (done)
> +			return done;
>  
>  		io = vdev->barmap[bar];
> -	}
>  
> -	if (bar == vdev->msix_bar) {
> -		x_start = vdev->msix_offset;
> -		x_end = vdev->msix_offset + vdev->msix_size;
> -	}
> +		if (bar == vdev->msix_bar) {
> +			x_start = vdev->msix_offset;
> +			x_end = vdev->msix_offset + vdev->msix_size;
> +		} else {
> +			x_start = 0;
> +			x_end = 0;
> +		}

There's a lot of semantic preference noise that obscures what you're
actually trying to accomplish here, effectively this has only
refactored the code to have separate calls to ..do_io_rw() for the ROM
vs other case and therefore pushed the unmap into the ROM case,
introducing various new exit paths.

>  
> -	done = vfio_pci_core_do_io_rw(vdev, res->flags & IORESOURCE_MEM, io, buf, pos,
> +		done = vfio_pci_core_do_io_rw(vdev, pci_resource_flags(pdev, bar) & IORESOURCE_MEM, io, buf, pos,

The line is too long already, now it's indented further and the
wrapping needs to be adjusted.

>  				      count, x_start, x_end, iswrite);
> -
> -	if (done >= 0)
> -		*ppos += done;
> -
> -	if (bar == PCI_ROM_RESOURCE)
> -		pci_unmap_rom(pdev, io);
> +	}
>  out:

Both goto's to this label were removed above, none added.  Thanks,

Alex

> +	if (done > 0)
> +		*ppos += done;
>  	return done;
>  }
>