Re: [Intel-gfx] [PATCHi v2] drm/i915: Enhanced disable access to stolen memory as a guest

[Daniel Vetter]

On Tue, Mar 28, 2017 at 01:28:43AM +, Zhang, Xiong Y wrote:
> > > Reviewed-by: Zhenyu Wang 
> > 
> > Entirely disabling stolen is rather massive, this stuff is supposed to
> > work ... There should be special RMRR mappings in the iommu to help the
> > guest access the stolen range correctly from the gpu.
> > 
> > Which machine where does this blow up on?
> > -Daniel
> [Zhang, Xiong Y] Yes. Stolen memory is protected by RMRR on host. But Qemu 
> couldn't support and don't have plan to support RMRR. Then EPT lack of 
> mapping for stolen memory, guest couldn't access it.
> The Qemu/Vfio is designed by Redhat engineers, Redhat has a white paper to 
> explain why Qemu don't support RMRR:
> https://access.redhat.com/sites/default/files/attachments/rmrr-wp1.pdf

I chatted with Joonas, and he dug out the commit that changed this:

commit c875d2c1b8083cd627ea0463e20bf22c2d7421ee
Author: Alex Williamson 
Date:   Thu Jul 3 09:57:02 2014 -0600

iommu/vt-d: Exclude devices using RMRRs from IOMMU API domains

The user of the IOMMU API domain expects to have full control of
the IOVA space for the domain.  RMRRs are fundamentally incompatible
with that idea.  We can neither map the RMRR into the IOMMU API
domain, nor can we guarantee that the device won't continue DMA with
the area described by the RMRR as part of the new domain.  Therefore
we must prevent such devices from being used by the IOMMU API.

Signed-off-by: Alex Williamson 
Cc: David Woodhouse 
Cc: sta...@vger.kernel.org
Signed-off-by: Joerg Roedel 

Please reference that commit (plus the whitepaper if you want to) in your
commit message, and resubmit it with a Fixes: and cc: stable lines. This
sounds like a bugfix that we need to backport.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCHi v2] drm/i915: Enhanced disable access to stolen memory as a guest

[Zhang, Xiong Y]

> > Reviewed-by: Zhenyu Wang 
> 
> Entirely disabling stolen is rather massive, this stuff is supposed to
> work ... There should be special RMRR mappings in the iommu to help the
> guest access the stolen range correctly from the gpu.
> 
> Which machine where does this blow up on?
> -Daniel
[Zhang, Xiong Y] Yes. Stolen memory is protected by RMRR on host. But Qemu 
couldn't support and don't have plan to support RMRR. Then EPT lack of mapping 
for stolen memory, guest couldn't access it.
The Qemu/Vfio is designed by Redhat engineers, Redhat has a white paper to 
explain why Qemu don't support RMRR:
https://access.redhat.com/sites/default/files/attachments/rmrr-wp1.pdf

> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCHi v2] drm/i915: Enhanced disable access to stolen memory as a guest

[Daniel Vetter]

On Mon, Mar 27, 2017 at 10:21:42AM +0800, Zhenyu Wang wrote:
> On 2017.03.24 18:23:44 +0800, Xiong Zhang wrote:
> > commit "04a68a3 drm/i915/gvt: Disable access to stolen memory as a guest"
> > isn't enough in GVT-d which will pass through IGD to guest and don't run
> > vgt code. While intel_vgpu_active() is true only when vgt code run on
> > host and guest in GVT-g.
> > 
> > v2:GVT-g may run in non qemu (Zhenyu)
> > 
> > Signed-off-by: Xiong Zhang 
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c| 1 +
> >  drivers/gpu/drm/i915/i915_drv.h| 1 +
> >  drivers/gpu/drm/i915/i915_gem_stolen.c | 4 ++--
> >  3 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c 
> > b/drivers/gpu/drm/i915/i915_drv.c
> > index 03d9e45..8b807a9 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -223,6 +223,7 @@ static void intel_detect_pch(struct drm_i915_private 
> > *dev_priv)
> > PCI_SUBVENDOR_ID_REDHAT_QUMRANET &&
> > pch->subsystem_device ==
> > PCI_SUBDEVICE_ID_QEMU)) {
> > +   dev_priv->run_on_qemu = true;
> > dev_priv->pch_type =
> > intel_virt_detect_pch(dev_priv);
> > } else
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h 
> > b/drivers/gpu/drm/i915/i915_drv.h
> > index a5947a4..ad95c87 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -2145,6 +2145,7 @@ struct drm_i915_private {
> > struct intel_uncore uncore;
> >  
> > struct i915_virtual_gpu vgpu;
> > +   bool run_on_qemu;
> >  
> > struct intel_gvt *gvt;
> >  
> > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c 
> > b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > index f3abdc2..6a011b0 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > @@ -409,8 +409,8 @@ int i915_gem_init_stolen(struct drm_i915_private 
> > *dev_priv)
> >  
> > mutex_init(_priv->mm.stolen_lock);
> >  
> > -   if (intel_vgpu_active(dev_priv)) {
> > -   DRM_INFO("iGVT-g active, disabling use of stolen memory\n");
> > +   if (dev_priv->run_on_qemu || intel_vgpu_active(dev_priv)) {
> > +   DRM_INFO("Running in guest, disabling use of stolen memory\n");
> > return 0;
> > }
> >  
> > -- 
> 
> Reviewed-by: Zhenyu Wang 

Entirely disabling stolen is rather massive, this stuff is supposed to
work ... There should be special RMRR mappings in the iommu to help the
guest access the stolen range correctly from the gpu.

Which machine where does this blow up on?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCHi v2] drm/i915: Enhanced disable access to stolen memory as a guest

[Zhenyu Wang]

On 2017.03.24 18:23:44 +0800, Xiong Zhang wrote:
> commit "04a68a3 drm/i915/gvt: Disable access to stolen memory as a guest"
> isn't enough in GVT-d which will pass through IGD to guest and don't run
> vgt code. While intel_vgpu_active() is true only when vgt code run on
> host and guest in GVT-g.
> 
> v2:GVT-g may run in non qemu (Zhenyu)
> 
> Signed-off-by: Xiong Zhang 
> ---
>  drivers/gpu/drm/i915/i915_drv.c| 1 +
>  drivers/gpu/drm/i915/i915_drv.h| 1 +
>  drivers/gpu/drm/i915/i915_gem_stolen.c | 4 ++--
>  3 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 03d9e45..8b807a9 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -223,6 +223,7 @@ static void intel_detect_pch(struct drm_i915_private 
> *dev_priv)
>   PCI_SUBVENDOR_ID_REDHAT_QUMRANET &&
>   pch->subsystem_device ==
>   PCI_SUBDEVICE_ID_QEMU)) {
> + dev_priv->run_on_qemu = true;
>   dev_priv->pch_type =
>   intel_virt_detect_pch(dev_priv);
>   } else
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index a5947a4..ad95c87 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2145,6 +2145,7 @@ struct drm_i915_private {
>   struct intel_uncore uncore;
>  
>   struct i915_virtual_gpu vgpu;
> + bool run_on_qemu;
>  
>   struct intel_gvt *gvt;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c 
> b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index f3abdc2..6a011b0 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -409,8 +409,8 @@ int i915_gem_init_stolen(struct drm_i915_private 
> *dev_priv)
>  
>   mutex_init(_priv->mm.stolen_lock);
>  
> - if (intel_vgpu_active(dev_priv)) {
> - DRM_INFO("iGVT-g active, disabling use of stolen memory\n");
> + if (dev_priv->run_on_qemu || intel_vgpu_active(dev_priv)) {
> + DRM_INFO("Running in guest, disabling use of stolen memory\n");
>   return 0;
>   }
>  
> -- 

Reviewed-by: Zhenyu Wang 

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