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

[Baolu Lu <baolu.lu@linux.intel.com>]

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