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

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Date:   Tue, 14 Jun 2022 09:36:16 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>,
        Steve Wahl <steve.wahl@....com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <jroedel@...e.de>,
        Kyung Min Park <kyung.min.park@...el.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 2022/6/14 04:57, Jerry Snitselaar wrote:
> 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?

Do you have any compilation errors or warnings?

Best regards,
baolu

> 
>> +	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
>>
>