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SubjectRe: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when TES=0
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On 11/14/23 11:14 AM, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> 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@linux.intel.com>
>> ---
>> 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.

Best regards,
baolu

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