linux-kernel - Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS

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Date:   Mon, 13 Jun 2022 13:57:34 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Steve Wahl <steve.wahl@....com>
Cc:     Joerg Roedel <jroedel@...e.de>,
        Kyung Min Park <kyung.min.park@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Will Deacon <will@...nel.org>,
        iommu@...ts.linux-foundation.org,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

On Thu, May 12, 2022 at 10:13:09AM -0500, 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@....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.
> 
>  drivers/iommu/intel/Kconfig | 6 ++++++
>  include/linux/dmar.h        | 6 +-----
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
> index 247d0f2d5fdf..fdbda77ac21e 100644
> --- a/drivers/iommu/intel/Kconfig
> +++ b/drivers/iommu/intel/Kconfig
> @@ -9,6 +9,12 @@ config DMAR_PERF
>  config DMAR_DEBUG
>  	bool
>  
> +config DMAR_UNITS_SUPPORTED
> +	int "Number of DMA Remapping Units supported"

Also, should there be a "depends on (X86 || IA64)" here?

> +	default 1024 if MAXSMP
> +	default 128  if X86_64
> +	default 64
> +
>  config INTEL_IOMMU
>  	bool "Support for Intel IOMMU using DMA Remapping Devices"
>  	depends on PCI_MSI && ACPI && (X86 || IA64)
> diff --git a/include/linux/dmar.h b/include/linux/dmar.h
> index 45e903d84733..0c03c1845c23 100644
> --- a/include/linux/dmar.h
> +++ b/include/linux/dmar.h
> @@ -18,11 +18,7 @@
>  
>  struct acpi_dmar_header;
>  
> -#ifdef	CONFIG_X86
> -# define	DMAR_UNITS_SUPPORTED	MAX_IO_APICS
> -#else
> -# define	DMAR_UNITS_SUPPORTED	64
> -#endif
> +#define	DMAR_UNITS_SUPPORTED	CONFIG_DMAR_UNITS_SUPPORTED
>  
>  /* DMAR Flags */
>  #define DMAR_INTR_REMAP		0x1
> -- 
> 2.26.2
>