linux-kernel - Re: [PATCH] vfio/cdx: add support for CDX bus

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Date:   Mon, 3 Apr 2023 15:28:09 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Nipun Gupta <nipun.gupta@....com>
Cc:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <git@....com>, <harpreet.anand@....com>, <michal.simek@....com>
Subject: Re: [PATCH] vfio/cdx: add support for CDX bus

On Mon, 3 Apr 2023 19:55:25 +0530
Nipun Gupta <nipun.gupta@....com> wrote:
> diff --git a/drivers/vfio/cdx/Makefile b/drivers/vfio/cdx/Makefile
> new file mode 100644
> index 000000000000..82e4ef412c0f
> --- /dev/null
> +++ b/drivers/vfio/cdx/Makefile
...
> +static int vfio_cdx_mmap_mmio(struct vfio_cdx_region region,
> +			      struct vm_area_struct *vma)
> +{
> +	u64 size = vma->vm_end - vma->vm_start;
> +	u64 pgoff, base;
> +
> +	pgoff = vma->vm_pgoff &
> +		((1U << (VFIO_CDX_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
> +	base = pgoff << PAGE_SHIFT;
> +
> +	if (region.size < PAGE_SIZE || base + size > region.size)
> +		return -EINVAL;
> +
> +	vma->vm_pgoff = (region.addr >> PAGE_SHIFT) + pgoff;
> +	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +
> +	return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> +			       size, vma->vm_page_prot);
> +}
> +
> +static int vfio_cdx_mmap(struct vfio_device *core_vdev,
> +			 struct vm_area_struct *vma)
> +{
> +	struct vfio_cdx_device *vdev =
> +		container_of(core_vdev, struct vfio_cdx_device, vdev);
> +	struct cdx_device *cdx_dev = vdev->cdx_dev;
> +	unsigned int index;
> +
> +	index = vma->vm_pgoff >> (VFIO_CDX_OFFSET_SHIFT - PAGE_SHIFT);
> +
> +	if (vma->vm_end < vma->vm_start)
> +		return -EINVAL;
> +	if (vma->vm_start & ~PAGE_MASK)
> +		return -EINVAL;
> +	if (vma->vm_end & ~PAGE_MASK)
> +		return -EINVAL;
> +	if (!(vma->vm_flags & VM_SHARED))
> +		return -EINVAL;
> +	if (index >= cdx_dev->res_count)
> +		return -EINVAL;
> +
> +	if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_MMAP))
> +		return -EINVAL;
> +
> +	if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_READ) &&
> +	    (vma->vm_flags & VM_READ))
> +		return -EINVAL;
> +
> +	if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_WRITE) &&
> +	    (vma->vm_flags & VM_WRITE))
> +		return -EINVAL;
> +
> +	vma->vm_private_data = cdx_dev;
> +
> +	return vfio_cdx_mmap_mmio(vdev->regions[index], vma);
> +}

I see discussion of MMIO_REGIONS_ENABLE controlling host access to the
device in mc_cdx_pcol.h.  Is a user of vfio-cdx able to manipulate
whether MMIO space of the device is enabled?  If so, what's the system
response to accessing MMIO through the mmap while disabled?  Is MMIO
space accessible even through calling the RESET ioctl?  Is there a
public specification somewhere for CDX?  Thanks,

Alex