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

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Tuesday, November 14, 2023 12:55 PM
> 
> On 11/14/23 12:45 PM, Tian, Kevin wrote:
> >> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Tuesday, November 14, 2023 11:14 AM
> >>
> >> On 11/14/23 11:14 AM, Tian, Kevin wrote:
> >>>> 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.
> >>
> >> There might be valid cases. The VT-d translation is turned on after all
> >> devices get probed.
> >>
> >
> > but I didn't get why there will be actual mapping changes before
> > vtd translation is enabled...
> 
> For an example, in iommu_create_device_direct_mappings(),
> iommu_flush_iotlb_all() is called after direct mappings are created.
> 

Okay.

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>