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

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Message-ID: <1a07a265-f834-4834-b9cb-5c7016ee9142@linux.intel.com>
Date:   Tue, 14 Nov 2023 11:13:37 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when
 TES=0

On 11/14/23 11:14 AM, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.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@...ux.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