Re: [PATCH 1/1] iommu/vt-d: PRS isn't usable if PDS isn't supported

[Baolu Lu <baolu.lu@linux.intel.com>]

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 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(-)

Queued for v6.18.