Re: [PATCH v2 1/5] iommu/vt-d: Separate page request queue from SVM

[Baolu Lu]

On 2024/9/18 16:20, Tian, Kevin wrote:
> > From: Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Saturday, September 14, 2024 1:50 PM
> >
> > On 2024/9/14 10:53, Tian, Kevin wrote:
> > > > From: Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> > > > Sent: Saturday, September 14, 2024 9:18 AM
> > > >
> > > > On 9/14/24 8:52 AM, Tian, Kevin wrote:
> > > > > > From: Joel Granados via B4 Relay
> > > > > > <devnull+j.granados.samsung.com@xxxxxxxxxx>
> > > > > >
> > > > > > From: Joel Granados<j.granados@xxxxxxxxxxx>
> > > > > >
> > > > > > IO page faults are no longer dependent on
> > CONFIG_INTEL_IOMMU_SVM.
> > > > > > Move
> > > > > > all Page Request Queue (PRQ) functions that handle prq events to a
> > new
> > > > > > file in drivers/iommu/intel/prq.c. The page_req_des struct is now
> > > > > > declared in drivers/iommu/intel/prq.c.
> > > > > >
> > > > > > No functional changes are intended. This is a preparation patch to
> > > > > > enable the use of IO page faults outside the SVM/PASID use cases.
> > > > > Do we want to guard it under a new config option e.g.
> > > > > CONFIG_INTEL_IOMMU_IOPF? it's unnecessary to allocate resources
> > > > > for the majority usages which don't require IOPF.
> > > > >
> > > > > Baolu?
> > > > The OS builder doesn't know if Linux will run on a platform with PRI-
> > > > capable devices. They'll probably always enable this option if we
> > > > provide it.
> > > hmm then why do we need a SVM option? In reality I haven't seen
> > > a platform which supports IOPF but no pasid/SVM. so the reason
> > > for whether to have an option should be same between IOPF/SVM.
> > >
> > > IMHO the point of options is to allow reducing footprint of the kernel
> > > image and many options are probably always enabled in distributions...
> > To be honest, I would hope to remove the SVM option some day. It's
> > nothing special except listening to an external notification and
> > synchronize the caches when the page table is updated.
> more than that... for each IOMMU the current code allocates 16 pages
> and 1 hwirq. Those are unnecessary burdens in majority deployments
> which don't support/require I/O page faults.

Yeah! I only focused on the kernel binary size but ignored these system
resources consumed by IOPF. Then, perhaps

diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index f52fb39c968e..847a5c43c9dc 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -97,4 +97,7 @@ config INTEL_IOMMU_PERF_EVENTS
          to aid performance tuning and debug. These are available on 
modern
          processors which support Intel VT-d 4.0 and later.

+config INTEL_IOMMU_IOPF
+       depends on IOMMUFD || INTEL_IOMMU_SVM
+
 endif # INTEL_IOMMU
diff --git a/drivers/iommu/intel/Makefile b/drivers/iommu/intel/Makefile
index c8beb0281559..c382307ae7aa 100644
--- a/drivers/iommu/intel/Makefile
+++ b/drivers/iommu/intel/Makefile
@@ -5,6 +5,7 @@ obj-$(CONFIG_DMAR_TABLE) += trace.o cap_audit.o
 obj-$(CONFIG_DMAR_PERF) += perf.o
 obj-$(CONFIG_INTEL_IOMMU_DEBUGFS) += debugfs.o
 obj-$(CONFIG_INTEL_IOMMU_SVM) += svm.o
+obj-$(CONFIG_INTEL_IOMMU_IOPF) += prq.o
 ifdef CONFIG_INTEL_IOMMU
 obj-$(CONFIG_IRQ_REMAP) += irq_remapping.o
 endif

?

Thanks,
baolu