On 9/24/26 5:50 PM, Jason Gunthorpe wrote:
On Mon, Sep 07, 2026 at 11:12:06PM -0500, Mario Limonciello wrote:
+EXPORT_SYMBOL_GPL(amd_iommu_enable_perfopt);
Last time we hardwired the GPU and IOMMU drivers together it was a
huge mess to undo.
Why does the GPU driver have to request this? Why can't the iommu
driver know that this is a special device that can use this magic fast
path and then auto set it when identity is asked for?
The reason was to allow an "opt-out" path on the GPU driver.
How does the GPU driver even know it is magic special?
See patch 2/2. GPU driver looks if it's an APU and it's in identity
mode. The special mode is only for the GPU in an APU. It shouldn't be
applied to anything else.
+ /*
+ * Restore ATS/PRI/PASID (and thus SVA) by re-homing the device onto its
+ * identity domain with the flag cleared, so a later bind without
PerfOpt
+ * sees a normally-capable device. See the locking note in
+ * amd_iommu_enable_perfopt().
+ */
And this is sort of a wrong thing in the driver, it shouldn't have ATS
turned on for identitiy mappings, and it certainly shouldn't have PRI
turned on until a PRI capable domain is attached.
Jason
amd_iommu_disable_perfopt() only re-applies the policy that was
previously set before PerfOpt.
If you would like I'll send a follow up patch to clarify this comment.
