linux-kernel - Re: [PATCH] drm/hyperv: Fix device removal on Gen1 VMs

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Date:   Fri, 19 Nov 2021 16:42:28 -0800
From:   Deepak Rawat <drawat.floss@...il.com>
To:     Mohammed Gamal <mgamal@...hat.com>, linux-hyperv@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, decui@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, daniel@...ll.ch, airlied@...ux.ie
Subject: Re: [PATCH] drm/hyperv: Fix device removal on Gen1 VMs

Thanks for the patch.

Reviewed-by: Deepak Rawat <drawat.floss@...il.com>

I will push this to drm-fixes, let me know otherwise.

Deepak

On Fri, 2021-11-19 at 12:29 +0100, Mohammed Gamal wrote:
> The Hyper-V DRM driver tries to free MMIO region on removing
> the device regardless of VM type, while Gen1 VMs don't use MMIO
> and hence causing the kernel to crash on a NULL pointer dereference.
> 
> Fix this by making deallocating MMIO only on Gen2 machines and
> implement
> removal for Gen1
> 
> Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic
> video device")
> 
> Signed-off-by: Mohammed Gamal <mgamal@...hat.com>
> ---
>  drivers/gpu/drm/hyperv/hyperv_drm_drv.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> index cd818a629183..9f923beb7d8d 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> @@ -225,12 +225,29 @@ static int hyperv_vmbus_remove(struct hv_device
> *hdev)
>  {
>         struct drm_device *dev = hv_get_drvdata(hdev);
>         struct hyperv_drm_device *hv = to_hv(dev);
> +       struct pci_dev *pdev;
>  
>         drm_dev_unplug(dev);
>         drm_atomic_helper_shutdown(dev);
>         vmbus_close(hdev->channel);
>         hv_set_drvdata(hdev, NULL);
> -       vmbus_free_mmio(hv->mem->start, hv->fb_size);
> +
> +       /*
> +        * Free allocated MMIO memory only on Gen2 VMs.
> +        * On Gen1 VMs, release the PCI device
> +        */
> +       if (efi_enabled(EFI_BOOT)) {
> +               vmbus_free_mmio(hv->mem->start, hv->fb_size);
> +       } else {
> +               pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT,
> +                               PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
> +               if (!pdev) {
> +                       drm_err(dev, "Unable to find PCI Hyper-V
> video\n");
> +                       return -ENODEV;
> +               }
> +               pci_release_region(pdev, 0);
> +               pci_dev_put(pdev);
> +       }
>  
>         return 0;
>  }