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SubjectRe: [PATCH v3] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting
On Thu, Jun 23, 2022 at 10:29:35AM +0800, Baolu Lu wrote:
> On 2022/6/22 23:05, 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.
>
> It's more reasonable to move it under INTEL_IOMMU, but the trouble is
> that this also stands even if INTEL_IOMMU is not configured.

My thought only was with it after the 'config INTEL_IOMMU' block and before 'if INTEL_IOMMU'
it would show up like:

[*] Support for Intel IOMMU using DMA Remapping Devices
(1024) Number of DMA Remapping Units supported <<<< NEW

>
> The real problem here is that the iommu sequence ID overflows if
> DMAR_UNITS_SUPPORTED is not big enough. This is purely a software
> implementation issue, I am not sure whether user opt-in when building a
> kernel package could help a lot here.
>

Is this something that could be figured out when parsing the dmar
table? It looks like currently iommu_refcnt[], iommu_did[], and
dmar_seq_ids[] depend on it.

Regards,
Jerry


> If we can't find a better way, can we just step back?
>
> Best regards,
> baolu

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