RE: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when TES=0

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Tuesday, November 14, 2023 9:11 AM
> 
> The latest VT-d spec indicates that when remapping hardware is disabled
> (TES=0 in Global Status Register), upstream ATS Invalidation Completion
> requests are treated as UR (Unsupported Request).
> 
> Consequently, the spec recommends in section 4.3 Handling of Device-TLB
> Invalidations that software refrain from submitting any Device-TLB
> invalidation requests when address remapping hardware is disabled.
> 
> Verify address remapping hardware is enabled prior to submitting Device-
> TLB invalidation requests.
> 
> Fixes: 792fb43ce2c9 ("iommu/vt-d: Enable Intel IOMMU scalable mode by
> default")
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/dmar.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> index a3414afe11b0..23cb80d62a9a 100644
> --- a/drivers/iommu/intel/dmar.c
> +++ b/drivers/iommu/intel/dmar.c
> @@ -1522,6 +1522,15 @@ void qi_flush_dev_iotlb(struct intel_iommu
> *iommu, u16 sid, u16 pfsid,
>  {
>  	struct qi_desc desc;
> 
> +	/*
> +	 * VT-d spec, section 4.3:
> +	 *
> +	 * Software is recommended to not submit any Device-TLB
> invalidation
> +	 * requests while address remapping hardware is disabled.
> +	 */
> +	if (!(iommu->gcmd & DMA_GCMD_TE))
> +		return;
> +

Is it a valid case to see such request when the iommu is disabled?
If not then let's add a WARN.