Re: [Intel-gfx] [PATCH] drm/i915: Force VT'd workarounds when running as a guest OS

[Zhenyu Wang <zhenyuw@linux.intel.com>]

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On 2020.10.19 11:15:23 +0100, Chris Wilson wrote:
> If i915.ko is being used as a passthrough device, it does not know if
> the host is using intel_iommu. Mixing the iommu and gfx causing a few
> issues (such as scanout overfetch) which we need to workaround inside
> the driver, so if we detect we are running under a hypervisor, also
> assume the device access is being virtualised.
> 
> Reported-by: Stefan Fritsch <sf@sfritsch.de>
> Suggested-by: Stefan Fritsch <sf@sfritsch.de>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Stefan Fritsch <sf@sfritsch.de>
> Cc: stable@vger.kernel.org
> ---
>  drivers/gpu/drm/i915/i915_drv.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 1a5729932c81..bcd8650603d8 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -33,6 +33,8 @@
>  #include <uapi/drm/i915_drm.h>
>  #include <uapi/drm/drm_fourcc.h>
>  
> +#include <asm/hypervisor.h>
> +
>  #include <linux/io-mapping.h>
>  #include <linux/i2c.h>
>  #include <linux/i2c-algo-bit.h>
> @@ -1760,7 +1762,9 @@ static inline bool intel_vtd_active(void)
>  	if (intel_iommu_gfx_mapped)
>  		return true;
>  #endif
> -	return false;
> +
> +	/* Running as a guest, we assume the host is enforcing VT'd */
> +	return !hypervisor_is_type(X86_HYPER_NATIVE);
>  }
>  
>  static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
> -- 

Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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