linux-kernel - Re: [PATCH] drm/amdgpu: do not use passthrough mode in Xen dom0

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Date:   Wed, 27 Apr 2022 10:47:36 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Lijo Lazar <lijo.lazar@....com>,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        Guchun Chen <guchun.chen@....com>,
        David Airlie <airlied@...ux.ie>,
        Bokun Zhang <bokun.zhang@....com>,
        Jingwen Chen <Jingwen.Chen2@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        "for 3.8" <stable@...r.kernel.org>,
        Victor Skvortsov <victor.skvortsov@....com>,
        Michel Dänzer <mdaenzer@...hat.com>,
        "open list:RADEON and AMDGPU DRM DRIVERS" 
        <amd-gfx@...ts.freedesktop.org>, Bernard Zhao <bernard@...o.com>,
        Alex Deucher <alexander.deucher@....com>,
        Candice Li <candice.li@....com>,
        Christian König <christian.koenig@....com>,
        Hawking Zhang <Hawking.Zhang@....com>
Subject: Re: [PATCH] drm/amdgpu: do not use passthrough mode in Xen dom0

Applied.  Thanks!

Alex

On Wed, Apr 27, 2022 at 3:12 AM Marek Marczykowski-Górecki
<marmarek@...isiblethingslab.com> wrote:
>
> While technically Xen dom0 is a virtual machine too, it does have
> access to most of the hardware so it doesn't need to be considered a
> "passthrough". Commit b818a5d37454 ("drm/amdgpu/gmc: use PCI BARs for
> APUs in passthrough") changed how FB is accessed based on passthrough
> mode. This breaks amdgpu in Xen dom0 with message like this:
>
>     [drm:dc_dmub_srv_wait_idle [amdgpu]] *ERROR* Error waiting for DMUB idle: status=3
>
> While the reason for this failure is unclear, the passthrough mode is
> not really necessary in Xen dom0 anyway. So, to unbreak booting affected
> kernels, disable passthrough mode in this case.
>
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1985
> Fixes: b818a5d37454 ("drm/amdgpu/gmc: use PCI BARs for APUs in passthrough")
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
> Cc: stable@...r.kernel.org
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> index a025f080aa6a..5e3756643da3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> @@ -24,6 +24,7 @@
>  #include <linux/module.h>
>
>  #include <drm/drm_drv.h>
> +#include <xen/xen.h>
>
>  #include "amdgpu.h"
>  #include "amdgpu_ras.h"
> @@ -710,7 +711,8 @@ void amdgpu_detect_virtualization(struct amdgpu_device *adev)
>                 adev->virt.caps |= AMDGPU_SRIOV_CAPS_ENABLE_IOV;
>
>         if (!reg) {
> -               if (is_virtual_machine())       /* passthrough mode exclus sriov mod */
> +               /* passthrough mode exclus sriov mod */
> +               if (is_virtual_machine() && !xen_initial_domain())
>                         adev->virt.caps |= AMDGPU_PASSTHROUGH_MODE;
>         }
>
> --
> 2.35.1
>