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SubjectRe: [PATCH v3] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting
On Wed, Jun 22, 2022 at 08:05:12AM -0700, Jerry Snitselaar wrote:
> On Wed, Jun 22, 2022 at 7:52 AM Baolu Lu <baolu.lu@linux.intel.com> wrote:
> >
> > On 2022/6/16 02:36, Steve Wahl wrote:
> > > To support up to 64 sockets with 10 DMAR units each (640), make the
> > > value of DMAR_UNITS_SUPPORTED adjustable by a config variable,
> > > CONFIG_DMAR_UNITS_SUPPORTED, and make it's default 1024 when MAXSMP is
> > > set.
> > >
> > > If the available hardware exceeds DMAR_UNITS_SUPPORTED (previously set
> > > to MAX_IO_APICS, or 128), it causes these messages: "DMAR: Failed to
> > > allocate seq_id", "DMAR: Parse DMAR table failure.", and "x2apic: IRQ
> > > remapping doesn't support X2APIC mode x2apic disabled"; and the system
> > > fails to boot properly.
> > >
> > > Signed-off-by: Steve Wahl<steve.wahl@hpe.com>
> > > Reviewed-by: Kevin Tian<kevin.tian@intel.com>
> > > ---
> > >
> > > Note that we could not find a reason for connecting
> > > DMAR_UNITS_SUPPORTED to MAX_IO_APICS as was done previously. Perhaps
> > > it seemed like the two would continue to match on earlier processors.
> > > There doesn't appear to be kernel code that assumes that the value of
> > > one is related to the other.
> > >
> > > v2: Make this value a config option, rather than a fixed constant. The default
> > > values should match previous configuration except in the MAXSMP case. Keeping the
> > > value at a power of two was requested by Kevin Tian.
> > >
> > > v3: Make the config option dependent upon DMAR_TABLE, as it is not used without this.
> > >
> > > drivers/iommu/intel/Kconfig | 7 +++++++
> > > include/linux/dmar.h | 6 +-----
> > > 2 files changed, 8 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
> > > index 39a06d245f12..07aaebcb581d 100644
> > > --- a/drivers/iommu/intel/Kconfig
> > > +++ b/drivers/iommu/intel/Kconfig
> > > @@ -9,6 +9,13 @@ config DMAR_PERF
> > > config DMAR_DEBUG
> > > bool
> > >
> > > +config DMAR_UNITS_SUPPORTED
> > > + int "Number of DMA Remapping Units supported"
> > > + depends on DMAR_TABLE
> > > + default 1024 if MAXSMP
> > > + default 128 if X86_64
> > > + default 64
> >
> > With this patch applied, the IOMMU configuration looks like:
> >
> > [*] AMD IOMMU support
> > <M> AMD IOMMU Version 2 driver
> > [*] Enable AMD IOMMU internals in DebugFS
> > (1024) Number of DMA Remapping Units supported <<<< NEW
> > [*] Support for Intel IOMMU using DMA Remapping Devices
> > [*] Export Intel IOMMU internals in Debugfs
> > [*] Support for Shared Virtual Memory with Intel IOMMU
> > [*] Enable Intel DMA Remapping Devices by default
> > [*] Enable Intel IOMMU scalable mode by default
> > [*] Support for Interrupt Remapping
> > [*] OMAP IOMMU Support
> > [*] Export OMAP IOMMU internals in DebugFS
> > [*] Rockchip IOMMU Support
> >
> > The NEW item looks confusing. It looks to be a generic configurable
> > value though it's actually Intel DMAR specific. Any thoughts?
> >
> > Best regards,
> > baolu
> >
>
> Would moving it under INTEL_IOMMU at least have it show up below
> "Support for Intel IOMMU using DMA Remapping Devices"? I'm not sure it
> can be better than that, because IRQ_REMAP selects DMAR_TABLE, so we
> can't stick it in the if INTEL_IOMMU section.
>
> Regards,
> Jerry

I have no qualms with Jerry's suggestion.

--> Steve Wahl

--
Steve Wahl, Hewlett Packard Enterprise

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