The specification, Section 7.10, "Software Steps to Drain Page Requests & Responses," requires software to submit an Invalidation Wait Descriptor (inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with the Invalidation Wait Completion Status Write flag (SW=1). It then waits for the Invalidation Wait Descriptor's completion.
However, the PD field in the Invalidation Wait Descriptor is optional, as stated in Section 6.5.2.9, "Invalidation Wait Descriptor":
"Page-request Drain (PD): Remapping hardware implementations reporting Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this field as reserved."
This implies that if the IOMMU doesn't support the PDS capability, software can't drain page requests and group responses as expected.
Do not enable PCI/PRI if the IOMMU doesn't support PDS.
Reported-by: Joel Granados joel.granados@kernel.org Closes: https://lore.kernel.org/r/20250909-jag-pds-v1-1-ad8cba0e494e@kernel.org Fixes: 66ac4db36f4c ("iommu/vt-d: Add page request draining support") Cc: stable@vger.kernel.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com --- drivers/iommu/intel/iommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..92759a8f8330 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -3812,7 +3812,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev) }
if (info->ats_supported && ecap_prs(iommu->ecap) && - pci_pri_supported(pdev)) + ecap_pds(iommu->ecap) && pci_pri_supported(pdev)) info->pri_supported = 1; } }
On Mon, Sep 15, 2025 at 02:29:46PM +0800, Lu Baolu wrote:
The specification, Section 7.10, "Software Steps to Drain Page Requests & Responses," requires software to submit an Invalidation Wait Descriptor (inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with the Invalidation Wait Completion Status Write flag (SW=1). It then waits for the Invalidation Wait Descriptor's completion.
However, the PD field in the Invalidation Wait Descriptor is optional, as stated in Section 6.5.2.9, "Invalidation Wait Descriptor":
"Page-request Drain (PD): Remapping hardware implementations reporting Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this field as reserved."
This implies that if the IOMMU doesn't support the PDS capability, software can't drain page requests and group responses as expected.
Do not enable PCI/PRI if the IOMMU doesn't support PDS.
After giving the spec another look, this is probably the way to go. However the PDS also mentions that DT must be set. Should we check ecap_dev_iotlb_support(iommu->ecap) as well?
Reported-by: Joel Granados joel.granados@kernel.org Closes: https://lore.kernel.org/r/20250909-jag-pds-v1-1-ad8cba0e494e@kernel.org Fixes: 66ac4db36f4c ("iommu/vt-d: Add page request draining support") Cc: stable@vger.kernel.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com
drivers/iommu/intel/iommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..92759a8f8330 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -3812,7 +3812,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev) } if (info->ats_supported && ecap_prs(iommu->ecap) &&
pci_pri_supported(pdev))
ecap_pds(iommu->ecap) && pci_pri_supported(pdev))
Should this be + ecap_dev_iotlb_support(iommu->ecap) && ecap_pds(iommu->ecap) && pci_pri_supported(pdev))
???
best
On 9/15/25 19:30, Joel Granados wrote:
On Mon, Sep 15, 2025 at 02:29:46PM +0800, Lu Baolu wrote:
The specification, Section 7.10, "Software Steps to Drain Page Requests & Responses," requires software to submit an Invalidation Wait Descriptor (inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with the Invalidation Wait Completion Status Write flag (SW=1). It then waits for the Invalidation Wait Descriptor's completion.
However, the PD field in the Invalidation Wait Descriptor is optional, as stated in Section 6.5.2.9, "Invalidation Wait Descriptor":
"Page-request Drain (PD): Remapping hardware implementations reporting Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this field as reserved."
This implies that if the IOMMU doesn't support the PDS capability, software can't drain page requests and group responses as expected.
Do not enable PCI/PRI if the IOMMU doesn't support PDS.
After giving the spec another look, this is probably the way to go. However the PDS also mentions that DT must be set. Should we check ecap_dev_iotlb_support(iommu->ecap) as well?
It has already been checked.
Reported-by: Joel Granados joel.granados@kernel.org Closes: https://lore.kernel.org/r/20250909-jag-pds-v1-1-ad8cba0e494e@kernel.org Fixes: 66ac4db36f4c ("iommu/vt-d: Add page request draining support") Cc: stable@vger.kernel.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com
drivers/iommu/intel/iommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..92759a8f8330 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -3812,7 +3812,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev) } if (info->ats_supported && ecap_prs(iommu->ecap) &&
pci_pri_supported(pdev))
ecap_pds(iommu->ecap) && pci_pri_supported(pdev))Should this be
ecap_dev_iotlb_support(iommu->ecap) && ecap_pds(iommu->ecap) && pci_pri_supported(pdev))???
ecap_dev_iotlb_support() has already been checked as it's part of the info->ats_supported check. The dependency chain is: ecap_dev_iotlb_support() -> ats_support -> pri_support.
Thanks, baolu
On Tue, Sep 16, 2025 at 09:58:14AM +0800, Baolu Lu wrote:
On 9/15/25 19:30, Joel Granados wrote:
On Mon, Sep 15, 2025 at 02:29:46PM +0800, Lu Baolu wrote:
The specification, Section 7.10, "Software Steps to Drain Page Requests & Responses," requires software to submit an Invalidation Wait Descriptor (inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with the Invalidation Wait Completion Status Write flag (SW=1). It then waits for the Invalidation Wait Descriptor's completion.
However, the PD field in the Invalidation Wait Descriptor is optional, as stated in Section 6.5.2.9, "Invalidation Wait Descriptor":
"Page-request Drain (PD): Remapping hardware implementations reporting Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this field as reserved."
This implies that if the IOMMU doesn't support the PDS capability, software can't drain page requests and group responses as expected.
Do not enable PCI/PRI if the IOMMU doesn't support PDS.
After giving the spec another look, this is probably the way to go. However the PDS also mentions that DT must be set. Should we check ecap_dev_iotlb_support(iommu->ecap) as well?
It has already been checked.
Yes. In intel_iommu_probe_device. Thx for the clarification.
Best
On 9/15/25 14:29, Lu Baolu wrote:
The specification, Section 7.10, "Software Steps to Drain Page Requests & Responses," requires software to submit an Invalidation Wait Descriptor (inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with the Invalidation Wait Completion Status Write flag (SW=1). It then waits for the Invalidation Wait Descriptor's completion.
However, the PD field in the Invalidation Wait Descriptor is optional, as stated in Section 6.5.2.9, "Invalidation Wait Descriptor":
"Page-request Drain (PD): Remapping hardware implementations reporting Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this field as reserved."
This implies that if the IOMMU doesn't support the PDS capability, software can't drain page requests and group responses as expected.
Do not enable PCI/PRI if the IOMMU doesn't support PDS.
Reported-by: Joel Granadosjoel.granados@kernel.org Closes:https://lore.kernel.org/r/20250909-jag-pds-v1-1-ad8cba0e494e@kernel.org Fixes: 66ac4db36f4c ("iommu/vt-d: Add page request draining support") Cc:stable@vger.kernel.org Signed-off-by: Lu Baolubaolu.lu@linux.intel.com
drivers/iommu/intel/iommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Queued for v6.18.
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