linux-kernel - Re: [RFC PATCH 3/9] vfio/pci: register a default migration region

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Message-ID: <20191205165515.3a9ac7b6@x1.home>
Date:   Thu, 5 Dec 2019 16:55:15 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        libvir-list@...hat.com, qemu-devel@...gnu.org, cohuck@...hat.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com,
        kevin.tian@...el.com, shaopeng.he@...el.com
Subject: Re: [RFC PATCH 3/9] vfio/pci: register a default migration region

On Wed,  4 Dec 2019 22:26:38 -0500
Yan Zhao <yan.y.zhao@...el.com> wrote:

> Vendor driver specifies when to support a migration region through cap
> VFIO_PCI_DEVICE_CAP_MIGRATION in vfio_pci_mediate_ops->open().
> 
> If vfio-pci detects this cap, it creates a default migration region on
> behalf of vendor driver with region len=0 and region->ops=null.
> Vendor driver should override this region's len, flags, rw, mmap in
> its vfio_pci_mediate_ops.
> 
> This migration region definition is aligned to QEMU vfio migration code v8:
> (https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg05542.html)
> 
> Cc: Kevin Tian <kevin.tian@...el.com>
> 
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> ---
>  drivers/vfio/pci/vfio_pci.c |  15 ++++
>  include/linux/vfio.h        |   1 +
>  include/uapi/linux/vfio.h   | 149 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 165 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index f3730252ee82..059660328be2 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -115,6 +115,18 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
>  	return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
>  }
>  
> +/**
> + * init a region to hold migration ctl & data
> + */
> +void init_migration_region(struct vfio_pci_device *vdev)
> +{
> +	vfio_pci_register_dev_region(vdev, VFIO_REGION_TYPE_MIGRATION,
> +		VFIO_REGION_SUBTYPE_MIGRATION,
> +		NULL, 0,
> +		VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_WRITE,
> +		NULL);
> +}
> +
>  static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev)
>  {
>  	struct resource *res;
> @@ -523,6 +535,9 @@ static int vfio_pci_open(void *device_data)
>  				vdev->mediate_ops = mentry->ops;
>  				vdev->mediate_handle = handle;
>  
> +				if (caps & VFIO_PCI_DEVICE_CAP_MIGRATION)
> +					init_migration_region(vdev);

No.  We're not going to add a cap flag for every region the mediation
driver wants to add.  The mediation driver should have the ability to
add regions and irqs to the device itself.  Thanks,

Alex

> +
>  				pr_info("vfio pci found mediate_ops %s, caps=%llx, handle=%x for %x:%x\n",
>  						vdev->mediate_ops->name, caps,
>  						handle, vdev->pdev->vendor,