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Message-ID: <2f2582df-fb56-4b46-8ce3-364879b34734@linux.intel.com>
Date: Thu, 30 Nov 2023 12:06:59 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
Will Deacon <will@...nel.org>,
Robin Murphy <robin.murphy@....com>,
Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when
TES=0
On 2023/11/30 4:10, Jason Gunthorpe wrote:
> On Tue, Nov 14, 2023 at 09:10:34AM +0800, Lu Baolu wrote:
>> 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(+)
> How did you get to the point where flush_dev_iotlb could even be
> called if the iommu has somehow been globally disabled?
>
> Shouldn't the attach of the domain compeltely fail if the HW is
> disabled?
>
> If the domain is not attached to anything why would flushing happen?
The VT-d hardware can be in a state where the hardware is on but DMA
translation is deactivated. In this state, the device probe process
during boot proceeds as follows:
1) Initialize the IOMMU contexts: This sets up the data structures that
the IOMMU uses to manage address translation for DMA operations.
2) Register the IOMMU devices: This registers the IOMMU devices to the
core. The core then probes devices on buses like PCI.
3) Enable DMA translation: This step activates DMA translation.
With regard to step 2), the call to iommu_flush_iotlb_all() in
iommu_create_device_direct_mappings() can potentially cause device TBL
invalidation when the VT-d DMA translation is deactivated.
Best regards,
baolu
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