netdev - Re: [PATCH v14 vfio 6/8] vfio/pds: Add support for dirty page tracking

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Date: Tue, 8 Aug 2023 16:27:18 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Brett Creeley <brett.creeley@....com>
Cc: <kvm@...r.kernel.org>, <netdev@...r.kernel.org>, <jgg@...dia.com>,
 <yishaih@...dia.com>, <shameerali.kolothum.thodi@...wei.com>,
 <kevin.tian@...el.com>, <horms@...nel.org>, <shannon.nelson@....com>
Subject: Re: [PATCH v14 vfio 6/8] vfio/pds: Add support for dirty page
 tracking

On Mon, 7 Aug 2023 13:57:53 -0700
Brett Creeley <brett.creeley@....com> wrote:
...
> +static int pds_vfio_dirty_enable(struct pds_vfio_pci_device *pds_vfio,
> +				 struct rb_root_cached *ranges, u32 nnodes,
> +				 u64 *page_size)
> +{
> +	struct pci_dev *pdev = pds_vfio->vfio_coredev.pdev;
> +	struct device *pdsc_dev = &pci_physfn(pdev)->dev;
> +	struct pds_vfio_dirty *dirty = &pds_vfio->dirty;
> +	u64 region_start, region_size, region_page_size;
> +	struct pds_lm_dirty_region_info *region_info;
> +	struct interval_tree_node *node = NULL;
> +	u8 max_regions = 0, num_regions;
> +	dma_addr_t regions_dma = 0;
> +	u32 num_ranges = nnodes;
> +	u32 page_count;
> +	u16 len;
> +	int err;
> +
> +	dev_dbg(&pdev->dev, "vf%u: Start dirty page tracking\n",
> +		pds_vfio->vf_id);
> +
> +	if (pds_vfio_dirty_is_enabled(pds_vfio))
> +		return -EINVAL;
> +
> +	/* find if dirty tracking is disabled, i.e. num_regions == 0 */
> +	err = pds_vfio_dirty_status_cmd(pds_vfio, 0, &max_regions,
> +					&num_regions);
> +	if (err < 0) {
> +		dev_err(&pdev->dev, "Failed to get dirty status, err %pe\n",
> +			ERR_PTR(err));
> +		return err;
> +	} else if (num_regions) {
> +		dev_err(&pdev->dev,
> +			"Dirty tracking already enabled for %d regions\n",
> +			num_regions);
> +		return -EEXIST;
> +	} else if (!max_regions) {
> +		dev_err(&pdev->dev,
> +			"Device doesn't support dirty tracking, max_regions %d\n",
> +			max_regions);
> +		return -EOPNOTSUPP;
> +	}
> +
> +	/*
> +	 * Only support 1 region for now. If there are any large gaps in the
> +	 * VM's address regions, then this would be a waste of memory as we are
> +	 * generating 2 bitmaps (ack/seq) from the min address to the max
> +	 * address of the VM's address regions. In the future, if we support
> +	 * more than one region in the device/driver we can split the bitmaps
> +	 * on the largest address region gaps. We can do this split up to the
> +	 * max_regions times returned from the dirty_status command.
> +	 */

Isn't this a pretty unfortunately limitation given QEMU makes a 1TB
hole on AMD hosts?  Or maybe I misunderstand.

https://gitlab.com/qemu-project/qemu/-/commit/8504f129450b909c88e199ca44facd35d38ba4de

Thanks,
Alex