Re: [PATCH v3] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

From: Jerry Snitselaar
Date: Wed Jun 22 2022 - 11:05:57 EST


On Wed, Jun 22, 2022 at 7:52 AM Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx> 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@xxxxxxx>
> > Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>
> > ---
> >
> > 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